NAT'L INST. OF STAND & TECH NIST

PUBLICATIONS

AlllOb 722D0A

NBSIR 75-928

The National Measurement

System for Mass, Volume and

Density

Paul E. Pontius, James R. Whetstone, and John A. Simpson

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

Final

May 1978

* 75-119

DEPARTMENT OF COMMERCE

)NAL BUREAU OF STANDARDS

NBSIR 75-928

THE NATIONAL MEASUREMENT

SYSTEM FOR MASS, VOLUME AND

DENSITY

Paul E. Pontius, James R. Whetstone, and John A. Simpson

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

Final

May 1978

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Or. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

CONTENTS

Page

TABLE OF CONTENTS i LIST OF FIGURES iii

LIST OF TABLES iii

0.0 EXECUTIVE SUMMARY 1 1.0 INTRODUCTION 3 2.0 STRUCTURE OF THE MEASUREMENT SYSTEM 4-33

2.1 Conceptual System 6

2.1.1 Mass 6

2.1.2 Volume 8

2.1.3 Density 9 2.2 Basic Technical Infrastructure '. . . . 9

2.2.1 Documentary Specification System 12 2.2.1.1 Standardization Institutions 12 2.2.1.2 Survey of Documentary Standards 14 2.2.2 Instrumentation System 16 2.2.2.1 Measurement Tools and Techniques 17 2.2.2.2 The Instrumentation Industry 19

2.2.3 Reference Data 20

2.2.4 Reference Material 23

2.2.5 Science and People 23

2.3 Realized Measurement Capabilities 25

2.3.1 Quality of Reference Standards 25

2.3.2 The Measurement Process 29

2.4 Dissemination and Enforcement Network 30

2.4.1 Central Standards Authorities 30

2.4.2 State and Local Offices of Weights and Measures. . . 30

2.4.3 Standards and Testing Laboratories and Services. . . 31 2.4.4 Regulatory Agencies 32

2.5 Organizational Input-Output Transactions Matrix 33

3.0 IMPACT, STATUS AND TRENDS OF MEASUREMENT SYSTEM 33-38

3.1 Impact of Measurements 33

3.1.1 Functional, Technological and Scientific

Applications 33

3.1.2 Economic Impacts —Costs and Benefits 36 3.1.2.1 Processes Relating to Quality of

Material 36

3.1.2.2 Processes Associated With Quality

Control and Regulation 36

3.1.2.3 Processes Associated With Preparations

of Objects or Materials 36

3.1.3 Social, Human, Man-on-the-Street Impacts 36

3.2 Status and Trends of the System 37 4.0 SURVEY OF NBS SERVICES 38-55

4.1 The Past 38

4.2 The Present—Scope of NBS Services 39

4.2.1 Description of NBS Services 39 4.2.1.1 Mass Measurement 39

4.2.1.2 Volumetric Measurements —Glassware 39 4.2.1.3 Metal Volumetric Standards 40

4.2.1.4 Density Measurements 40

4.2.1.5 Measurement Assurance Program 40

4.2.1.6 Office of Weights and Measures 40

4.2.2 Users of NBS Services 41
CONTENTS

Page

4.2.3 Alternate Sources *. . . . 42

4.2.4 Funding Sources for NBS Services 45

4.2.5 Mechanism for Supplying Services 45

4.3 Impact of NBS Services 46

4.3.1 Economic Impact of Major User Classes 46

4.3.2 Technological Impact of Services 48

4.3.3 Pay-off from Changes in NBS Services 50

4.4 Evaluation of NBS Program 51 4.5 The Future 53

5.0 SUMMARY AND CONCLUSIONS 54

References 55-56

Appendix A. METHODOLOGY OF THE STUDY 57-59

Appendix B 60-65

References 66

i i
LIST OF FIGURES

Page

Figure 1: Measurement Process Infrastructure 5

Figure 2: Infrastructure Associated with the Metric 5

Figure 3: Voluntary Standards Infrastructure 7

Figure 4: Practical Hydrometer Scales 13

Figure 5: Mass Customer Profile (Major SIC Groups) 43

Figure 6: Mass Customer Profile (Three Digit SIC Groups) 43

Figure 7: Volume Customer Profile (Two and Three Digit SIC Groups) ... 44

Figure 8: Density Customer Profile (Two and Three Digit SIC Groups) . . 44

LIST OF TABLES

Table 1: Voluntary Standards Organizations 8

Table 2: Industrial Effort Relating to Mass, Volume and Density .... 21

Table 3: Commercial Weighing Devices in Use 22

Table 4: Devices Used in States' Weights and Measures Activities. ... 22

Table 5: Tolerances for Commercial Test Weights 27

Table 6: Typical Commercial Scale Tolerances 28

Table 7: Typical Measurement Uncertainties 29

Table 8: Summary for Users of NBS Calibration Services 47

Table 9: Petroleum Measurement Commitment 49

i i i
I

I
THE NATIONAL MEASUREMENT SYSTEM FOR MASS, VOLUME AND DENSITY

Paul E. Pontius, James R. Whetstone, and John A. Simpson

National Bureau of Standards

Mass, a property of all matter, is

unique in the sense that the concept is

generally deduced from the motion of a body under the influence of an applied

force. It is for this reason the mass unit for measurements over the range of

objects which can be physically handled

is now, and for some time to come will

continue to be, embodied in an artifact

standard. The mass of one object with

respect to another is deduced from a comparison of the gravitational forces

acting on the two objects. The additive

nature of mass makes it possible to con- struct appropriate subdivisions and

multiples of a single defining artifact.

The present mass unit, the International

Prototype Kilogram, is one of the Base

Units of the International System of

units. Access to the unit is provided by

Bureau International des Poids and Mesures

(Sevres, France) through prototype kilogram

replicas of the unit. Prototype Kilograms

No. 20 and No. 4 provide such access for

the United States, and are in turn the

basis for the U.S. practical mass scale as established by the ni chrome kilograms Nl and N2.

Volume is a quantity derived from the

length unit. It is inseparably coupled

with mass. The intent of the founders of

the Metric System was that one cubic decimeter of water at maximum density have a mass of one kilogram. The realization was

proven to be imperfect, thus introducing

for a period of time the liter as a volume

unit. (The current unit for volume is the

cubic meter). Precise mass measurement

requires a knowledge of the displacement

volume of the objects being compared.

Hydrostatic weighings are used to (a)

determine the displacement volume ratio

relative to an object with displacement

volume established by direct measurement

and (b) displacement volume relative to

a known density of the fluid.

Density is defined as mass per unit

volume. Density is a property of

interest for a variety of fluid mixtures.

The density of a fluid in conjunction

with mass measurement is a means to determine the containment volume of a variety of volumetric standards. Mass and

volume are both used to determine quantity

of material. Density is usually considered

1

to be a property of a material, however,

such extension requires an assumption on the homogenity of the sample measured.

Considering that most of the measurement

processes within the mass, volume and

density measurement systems are based on economic compromise rather than technological capabilities, it is presumptuous to assume that NBS has any substantial impact

on the total system. On the other hand,

NBS, by providing a means for access to the unit, is generally considered to be

a partner in all measurement activity.

Consistency of results commensurate with

requirements is a fundamental to all of

the activities the system supports. Resolution of inconsistencies, by referral measurements, by suggested process modification, or by basic changes in measurement

concept is the essential support to the

system provided by NBS.

In spite of the size of the system, it

appears to be in almost complete control

and operating to the general satisfaction

of all concerned. There are several reasons for this: (1) mass standards are intrinsically stable so that the unit once injected into a subsystem remains reasonably consistent; (2) the instruments used

are reliable; and (3) the size of large

subsystems concerned with voluntary standards, weights and measures activities,

government requirements, etc., result in

inertia with respect to change. Through

the mechanism of Measurement Assurance

Programs, NBS or any other interested

party, can test the effectiveness of a given subsystem relative to the intended

use of the measurement results. The

same medium provides a means for a running

audit of the subsystem to insure that

stability is not lost.

With the advent of the NBS-2 kilogram

comparator the precision of measurement

has reached the point where factors

affecting the short term stability of the

defining artifact can be studied. These

factors include cleaning procedures, moisture films and environmental contamination.

Problems associated with the air density

algorithm, e.g., oversimplification and

non-uniformity, introduce small offsets

in the practical mass scales of the various countries. These offsets, too small to be of concern in most weighing
operations, do not affect the consistency of

practical measurements in a given country.

Resolution of the problem, however, is

important in support of work on fundamental

physical constants.

There are certain identifiable

constituencies within the system which rely

exclusively on NBS services. Support to the State Weights and Measures activities,

coordinated by the NBS Office of Weights

and Measures, extends to about 84,000,000

weighings in supermarket chains alone,

which in part supports a $145,100,000 a year industry which provides the needed

weighing devices. The petroleum industry

has a worldwide investment of $1,800,000,000

in volume measurement facilities at 650,000

sites, manned by 50,000 full time personnel. Each "barrel" is measured on the

average of 12 times between the well head

and the consumer, with either custody

transfer or accountability between each

pair of measurements. All measurements on local or imported crude and products are

based on NBS calibration of metal volumetric provers. In the beverage industry,

approximately $2,500,000 is expended

annually for density measurements in the

production of $15,400,000,000 of products.

NBS is providing support in the development of procedures for both custody transfer and accountability of nuclear material.

The Mass Measurement Assurance Program provides direct support to the Department of

Defense measurement systems, measurement

systems within the nuclear and aerospace

industries, and to manufacturers of

precise weighing equipment.

Problems in the interface between the

Mass and Volume Section and the rest of

the measurement system are, in general,

matters of judgment. The section, recognizing the service roll of measurement, has

worked diligently to establish and maintain

a line of communication with the individual

users (a non-coherent constituency). Such

an approach requires not only an understanding of measurement process limitations

but also a clear definition of what is to be expected from the measurement effort.

The latter requirement is the most difficult, and where it has been possible to define acceptable limits relative to a particular undertaking there has been

visible evidence of success, e.g., savings

to the Food and Drug Administration relative to the calibration of glassware, the

adoption of measurement assurance procedures within the nuclear weapons complex,

and the efforts supporting accountability

and safeguarding of nuclear materials.

Assistance provided to large numbers of users through consultation generally

relates to specific problems, the

resolution of which has no visibility.

Generally, most of these problems relate to specifying what the measurement is supposed

to accomplish and there are those who

expect NBS to address his particular

problem, however ill defined.

On the other hand, there are pressures

to work through an interface (identifiable

constituency) both from within NBS and

from other sources. Working through an interface tends to isolate NBS from practical measurement problems. Interfacing

through a system of facilities which are primarily regulatory raises the question

as to whether such a system can provide

advice and guidance with regard to methods

and procedures without compromising its

regulatory function. The legalization of

all measurements, as proposed by the International Organization for Legal Metrology,

diverts attention from the measurement

result to traceability of the unit. In some instances, the consumer of measure- ment data is relieved from the burden of

proving that the results are adequate for

the intended purpose. In other instances,

there is an added burden of not only proving that the measurements are not only

adequate but also legal.

The above listed problems not withstanding; the discharge of NBS responsibilities in the area of mass, volume and

density, is judged to be satisfactory.

Except for the maintenance of certain staff

skills, the level of effort now displayed

results in slow but steady progress. The

nature of the services provided and the

role of the section will change as its

aging staff moves into retirement. The course of activities for the future

includes support to the system as it exists

at the time, and a continuing effort to improve the efficiency of measurement.
THE NATIONAL MEASUREMENT SYSTEM FOR MASS, VOLUME AND DENSITY

Paul E. Pontius, James R. Whetstone, and John A. Simpson

National Bureau of Standards

1. INTRODUCTION

Weighings for purposes of trade were made

at least as far back in time as the Early

Bronze Age and a well developed system of

standards and enforcement of standards was

in effect in Egypt by the second dynasty.

The use of the balance—as a symbol of fairness and justice —dates from the same mists

of antiquity [1]. While it was common knowledge that early governments used one set of

weights in the collection of goods for taxes

and another to disperse goods for services,

by simply interchanging the loads on the

balance pans, it was easy to demonstrate

that there was nothing wrong with the balance. In normal commerce, other than the

usual haggling over the details of the

transaction, the measurement process worked

well. However, with the first technological

advance which made weighings rapid and convenient, the steelyard thought to be introduced by the Romans, the situation changed.

The buyer was at the complete mercy of the

seller who could alter the instrument at

will, changing either the sliding poise, or the lever ratio. The widespread usage of

the steelyard in commerce was the genesis of

regulatory activities relating to weights

and weighing devices. It was the diversity

of local units, staunchly defended by the

tradesmen, that ultimately led to the development of the metric system of measurement

uni ts. Mass, in the context of mass measurement,

is based on physical laws formulated by

Newton [2], thus relative to the history of

weighing, and even the metric system, the

concept of mass is a recent one. Because of

the size of the solar system, Newton could

consider the planets and their satellites as points in the vacuum of space [3]. The con- cept of mass was essential to the formulation of his laws of motion. As a consequence,

mass cannot be measured directly in the

normally encountered environment.

For example, a balance, contrary to popular opinion, is a force comparison device

which cannot separate the gravitational

force acting on the object from the buoyant

effects of the atmosphere [4]. While one

can compare these forces to a very high precision, an algorithm must be employed to separate the two effects. This algorithm must

incorporate knowledge of the volume or density of the objects of interest as well as the density of the surrounding environment.

The qualities of mass, volume, and density

are related by the following definition:

MASS = VOLUME X DENSITY

One can determine one of these quantities if

the other two are known, e.g., the mass of

petroleum contained in a tanker can be determined from measurements of tank volumes

and petroleum density.

Maintenance of the unit of mass is, by the

Treaty of the Metre, the responsibility of

the Bureau Internationale des Poids et Mesures (BIPM). The responsibility for

maintenance of the base unit for mass and

the units for volume and density in the

United States is one of the oldest and most

basic missions of NBS. It remains a unique

responsibility since the mass unit is the

only Systeme Internationale (SI) unit which

in principle is not independently reproducible. Of the two Prototype Kilograms designated No. 4 and No. 20, received by the U.S.

under the Treaty of the Metre, Prototype

Kilogram No. 20 is the de facto United

States' unit of mass [5]. In reality, K4

and K20 are merely a mechanism for transferring a defined unit from one mass measurement system to another.

The derived unit of volume is now ex- pressed as length cubed. High precision

measurements of artifact displacement, or containment, volumes are determined from

length measurements. Such measurements are complex and rarely done, e.g., the work of

Cook [6,7] in measuring the density of mercury and that of Bowman, Schoonover and

Carroll in measuring the density of single

crystal silicon [8]. Practical measurements of displacement volumes use Archimedes

Principle, e.g., hydrostatic weighing in a fluid of known density.

Practical volumetric measures are vessels

whose volume is defined by weighing the vessel filled and empty, using a liquid of

known density. This operation inextricably

ties volume measurements to mass and density.

Where weighing operations are impossible,

such as in determining the capacity of large

volume tanks, direct dimensional measurements ("strapping") are used [9]. In these
cases, the errors normally encountered in

the length measurements are very small relative to the total volume of the tank.

The derived unit of density is currently

expressed as kilograms per cubic meter [10].

(In this case the SI unit is so large that

it has little practical meaning.) By far,

the majority of density measurements are

made for determination of the characteristics of substances in the liquid phase. A variety of arbitrary units are used, each

associated with a particular class of

liquid. The simplicity and precision of

the hydrometer is a practical means of

quality control for any products produced or marketed in liquid form, ranging from milk

to alcohol -water mixtures and from petroleum and its products to paints and acids.

Derived units involving force, e.g.,

direct force measurements, pressure measurements, electric field strength measurements,

are directly tied to mass measurement since mass is one of the base SI units. Each of

these areas is covered in other surveys,

nonetheless, the consistency within

and between these seemingly diverse fields

is directly related to the characterization

and dissemination of the mass unit.

Measurements of mass, volume, and density

are undoubtedly the most pervasive measurements performed in the world. Weighing operations are involved in activities ranging

from teaching addition in the elementary

grades to establishing the mass of a testing

device for use in determining the mass and

center of gravity of space vehicles and mass determination of objects used in current NBS

measurements of the universal gravitational

constant, G. In present day commerce, almost

all commodities are priced by weight, as are materials more precious than gold and cheaper

than dirt. Most physical and chemical processes are mass based. Chemical reactions, as well as the energy of nuclear reactions,

depend on mass ratios. Moreover, techniques

exist for conveniently performing weighings

over a range of 10 , literally, almost

nothing is too large or too small to be

weighed or to be similarly described through

the related properties, volume and density.

The almost infinite number of measurements of mass, volume, and density in the

United States tie to the Mass and Volume

Section of NBS in many different ways. In some cases the relation is established by

legal, or contractual, requirements. In other cases, the relation is either a matter

of necessity or of convenience. In some cases

the link between the U.S. Prototype Kilogram

and the point of judgment as to the acceptability of a given measurement relative to a specified requirement is through a hierarchy

of calibration laboratories. In other cases

the link is as short as is practicable. Each

route has its own unique characteristics.

The ultimate goal in any case is to obtain

a consistency of measurement compatible with

the manner in which the measurement is to be

used [11].

2. STRUCTURE OF THE MEASUREMENT SYSTEM

The commonality of certain elements in

specific measurement processes provides a logical basis for ordering groups of measurement processes into systems and subsystems.

To illustrate the ways in which the system is

"tied" together, figure 1 is a diagram of the

factors which affect the design and operation

of a specific measurement process. The task

requirements, which arise from the desire for

success, or the consequences of failure, are the basis for the details of the process.

These requirements, as perceived at the mea- surement level, establish the specific process

and procedural details. In operation, there

is a value judgment for each measurement

accept, scrap or rework items, or remeasure.

In the end, the item and result pass on to others and in combination with many other

elements, i.e. results from other measurement

processes, contractual requirements, entrepreneurial judgments, etc., constitute the

completion of the task. Economic factors,

success/failure ratio, changes in the con- sequences of failure, and changing technology are all "feedback" factors contributing

to refinement of process detail.

The one element common to all mass, volume

and density measurement processes is the con- ceptual basis for the measurement. This element, however, is more devisive that adhesive

relative to the total system. For example,

as the task requirements, either real or perceived, approach the limit of measurement

capabilities, each step in figure 1 must be

treated explicitly—not only relative to the

specific process but also relative to the

other. elements contributing to the accom- plishment of the task. Those who work in this area become, by necessity, "understanding"

oriented. In contrast, when the requirements

are modest with respect to capabilities, many

of the steps can be treated implicitly and

those who work in this area become

"procedure" oriented. In the first instance,

the interest is in "how much," i.e. the mass

of an object, the volume of a tank, or the

density of a material. In the latter

instance, the interest is in how much one is

in error if he assumes that the mass of an adjusted weight is 1 kilogram, or the

capacity of a "certified" prover is 1 gallon,

and so on. The most visible common element is the need

for access to a consistent set of metrics.
Another common element, which to date has no identifiable bureaucratic structure, relates

to the availability of adequate instrumentation. Finally there is a commonality in the

basis for the value judgment, particularly

where there are many processes engaged in the same or similar tasks, and where the measurement requirements are modest. The identifiFigure 1

able bureaucratic infrastructures relate to providing access to consistent metrics adequate for the task at hand, and to the value

judgments for similar measurements (voluntary

standards )

.

The infrastructure related to the metric

is shown in figure 2. All who have need have

INFRASTRUCTURE OF THE MEASUREMENT PROCESS

CONCEPT

SCIENTIFIC AND

TECHNICAL BASE

MEASUREMENT PROCESS

INSTRUMENT

PROCEDURE

METRIC

ITEM RESULT

ERROR

LIMIT

SCRAP AND

REWORK

DISPOSITION

VALUE

JUDGEMENT

PERCEIVED

REQUIREMENTS

TASK

REQUIREMENTS

ACCEPT

SUCCESS

OTHER TOTAL

ELEMENTS TASK

FAILURE

REFINEMENT

CONSEQUENCE

Figure 2 INFRASTRUCTURE OF THE METRIC

DEFINITION OF UNITS

t — BIPM*

(KILOGRAM)

USERS (A)

USERS (B)

NAT. LABS

OF

OTHER

NATIONS

J

^(REF^DATA) |

CALIBRATIONS

MASS

VOLUME

DENSITY

PRECISION EQPT.

MFR'S.

USERS (C)

BIPM = International Bureau of Weights and Measures, Sevres, France

OWM = NBS Office of Weights and Measures
access to adequate mass standards, either

from NBS and similar laboratories of other

nations, and in some cases, directly from

BIPM, or from other sources served by the

echelon shown. The first level dissemination

from NBS provides access to those with real

needs (USERS (A)), or perceived needs (USERS

(B)), which require direct access to national

standards. Precision equipment manufacturers

are also served. These in turn provide instruments and standards which are themselves

adequate for USERS (C). The industrial or- ganizations served in turn provide services

for a restricted set of users (USERS (R)),

generally limited to groups within the

particular organizations. Government laboratories, usually organized in hierarchial

echelon systems, also provide access to a restricted set of users. Finally, through

the Office of Weights and Measures, the state

laboratories provide services for their

inspections and in most cases to unrestricted

users, USERS (C). It should be noted that

both USERS (B) and USERS (C) include equipment manufacturers serving measurement areas

in which the requirements are modest.

The infrastructure associated with value

judgments; i.e. voluntary standards, regulations, etc., is considerably more complex.

The task is to establish a consensus agreement between the user-supplier, or the

regulator-regulated, as to what constitutes

an adequate measurement under a specific set

of conditions. The procedural steps leading

to a voluntary standard are shown in figure 3. The time span from start to general acceptance

is often in excess of 10 years. If the standard is in response to a regulatory requirement, the regulator may reject the entire

effort at any time. Obviously, once a standard becomes an accepted practice, it is ex- tremely difficult to make substantial changes

in spite of the fact that most standardizing

organizations require periodic review. The

standardizing organizations, with interest

in mass, volume and density measurements

are shown i n table 1

The structures described in figures 1,2,

and 3 are frameworks within which one can discuss various aspects of mass, volume,

and density measurement. The actual measurement system is far more complex. Unlike mea- surement systems which originated around

the turn of this century or later, mea- surements of mass, volume and density started

with the dawn of technology. These measurements are necessary to the accomplishment of

about every human endeavor, be it by an individual, a profession, or by a society. Fundamental to these accomplishments are measurement processes that work well enough for the

intended purposes. Where the resulting

processes are adequate, regardless of being

ill conceived, there is little to be gained

by imposing change. On the other hand,

technological progress may eventually

dictate requirements beyond the capabilities

of currently accepted practices, at which

time the old processes must be discarded and

a new and more appropriate one devised. Thus

because of the diversity of requirements at

any point in history there are (a) subsystems

which are stable with formal infrastructures;

(b) existing processes which, for various

reasons, are undergoing change with resulting

pressures on existing infrastructures; and

(c) processes being developed for emerging re quirements which are not as yet sufficiently

stable to permit the development of a formal

i nf rastructure.

2.1 Conceptual System

2.1.1 Mass

It is very difficult to construct a conceptual mass measurement system which would

be acceptable at all levels of interest.

From the beginning, and even now, most

weighings are associated with determining

quantity of material. Highly developed

weighing devices were widely used long before the reasons why such instruments were

successful were understood. The concept of mass does not exist without motion. Few,

however, would interpret the simple act of

placing a weight on a balance pan as motion.

Mass and force are inseparable, but an intellectual separation has been maintained

by definitions, e.g. mass is measured by a balance; force is measured with a spring.

While it is only necessary for a conceptual

system to be logically correct, there are good reasons for it to also reflect reality.

Few are motivated to pursue measurement

detail beyond an understanding of some conceptual system. Decisions are then made

on the basis of this understanding. If the

concept as perceived is in error, then the

decision may also be in error. The mass of a body is revealed by a body's resistance to change in state of

motion, i.e. inertia, or by the fact that a force of attraction exists between any two

bodies, that force being proportional to the

product of their masses and inversely proportional to the square of the distance between their mass centers, i.e. gravitation.

For all practical purposes, the same property of a body is responsible for both effects, thus consistent measurements systems

can be constructed using either effect.

Mass measurements on, or near the surface

of, the earth are based on gravitational

effects. Body mass changes of astronauts in

orbit were measured with systems based on
inertia! effects [12]. For a conceptual mass measurement system, it is sufficient to state simply that mass is one property of

any object.

Figure 3 INFRASTRUCTURE OF THE VOLUNTARY STANDARD PROCESS

IDENTIFY

REQUIREMENT

DEVELOP

TECHNOLOGY

TENTATIVE

STANDARD *]

TEST AND

EVALUATE

DRAFT

STANDARD

SUBMIT FOR

REVIEW

RESOLVE

COMMENTS

COMMITTEE

OF

INTERESTED

PARTIES

PUBLISH AND

DISSEMINATE

TEST

GENERAL

ACCEPTANCE

I

ALL

INTERESTED

l PARTIES

REVIEW

The traditional concept of mass equality,

"Two bodies have equal mass if, when placed

on the opposite pans of a "perfect" equal arm balance, result in the balance arms being horizontal," or paraphrases thereof,

has been a serious retardant to the understanding of mass, and mass measurement, and

the development of instrumentation. If one

accepts that mass is a unique property of an object, then, for the purpose of mass measurement, the object can be considered as a mass point located at the mass center of the

object. For two such mass points, if the

attractive gravitational forces at the same location in the earth's gravity field are

equal, then the two points have equal mass

properties. If the response of the two points to the application of a given force

is the same, the points also have equal mass properties.

For mass measurements in the earth's

gravity field, any force measurement device

with sufficient resolution, be it a traditional two pan balance, a nonsymmetric one

pan balance, an elastic device, a pressure

device, or whatever, is a candidate for a mass measuring instrument. Over the past

ten years, the traditional equal arm balance

has lost its position of prominence, even at

the highest level of mass measurement, that

of providing access to the International

Prototype Kilogram [13]. There are now a variety of high technology weighing devices

which are convenient to use and are adequate

for practically all requirements.

To complete the conceptual measurement

system, one must be able to extend or subdivide the unit, i.e. one needs a definition for addition. For a collection of

objects fixed relative to each other, there

is a unique point at which the total mass of

the collection can be considered to be con- centrated. In terms of measurement, this is

just another mass point, differing only in

quantity. It remains only to have the force sensor respond to the gravitational force

acting at this point. Simply stated, the mass of two objects together on a balance

pan is the sum of the masses of the individual objects. In reality, considerable care

is exercised in the design, construction,

and operation of weighing devices to assure

that with a single object, or a collection

of objects on the "pan," so to speak, the

effective mass center of the "pan" load has

a fixed position relative to the force sen- sor and the direction of the gravitational

field.

Considering an object, or collection of

objects, as a mass point in the concept introduces ambiguities in the realization of

the measurement. When these discrepancies

are important relative to the intended

7
Table 1. Standardizing Organizations with Interest in Mass, Volume and Density

Organization

International

Treaty of the Meter (BIPM)

International Standards Organization (ISO)

International Organization for Legal

Metrology (OIML)

Government and National

Department of Defense (DoD)

General Services Administration (GSA)

Nuclear Regulatory Commission (NRC)

American Society for Testing

Materials (ASTM)

American National Standards Institute (ANSI)

Professional

National Conference of Weights and

Measures (NCWM)

National Conference of Standards

Laboratories (NCSL)

American Petroleum Institute (API)

Scientific Apparatus Manufacturers

Association (SAMA)

Institute for Nuclear Materials

Management (INMM)

Classification

Treaty

Suppliers

Treaty

Government

Government

Government

(1)

(1)

(2)

(2)

Suppliers

Suppliers

Suppliers

Area of Interest

Units

Marketing

Legal Metrology

Procurement

Procurement

Material Control

Procedures, Materials,

Instruments, Artifacts

Artifacts, Instruments,

Procedures

Procedures, Administration

Petroleum Products

Apparatus

Nuclear Materials

Control

(1) Requires equal participation between users and suppliers

(2) Users and suppliers participate

usage of the result, a treatment of the ap- propriate ambiguities must be included in

the definition of equality. The major am- biguities are associated with the displacement volumes, air density, surface finish,

and the response of the surface of the objects to changes in environment, i.e., corrosion, moisture layers, etc. In some

instances, the difference in the position

of the mass centers of the objects being

compared, relative to the mass center of the

earth must also be considered.

2.1.2 Volume

The concept of volume is the quantity of

three dimensional space enclosed by a closed

boundary surface. Therefore, its dimensions,

as a derived unit, are those of length raised

to the third power. Volume is an additive

quantity. The major ambiguities of concern

in the realization of the measurement are associated with definition of the closed

boundary surface and temperature. For each

material, volumetric changes with temperature change are related to length changes

with temperatures for that material (usually

expressed as volumetric coefficient of

expansion)

.

Displacement volumes can be computed from

direct measures of the exterior dimensions

of solid objects. However, unless the objects are of very uniform geometry, the re- sults are relatively crude. When this

method is used, the geometry of the objects

is generally limited (cube, cylinder or sphere) with surface finish adequate for

length measurements by interf erometry. Vol- ume determinations by length measurement are

usually limited to two classes of measurement: those associated with determining the

density of various reference liquids, e.g. water and mercury, or those associated with

very large volumes, e.g. large objects and

liquid storage tanks.

Precise displacement volumes of a variety

of forms can be obtained by Archimedes'

Principle, e.g., hydrostatic weighing in a fluid of known density. Volumetric coefficients of expansion enter in two places: for

the object and for the density of the fluid.

The surfaces of the object must be compatible with the fluid so that the boundaries

remain clearly defined without causing the mass of the object or the density of the

fluid to change. One of the largest ambiguities in this method is associated with air

bubbles which are entrapped on the surface
of the submerged object which, in turn, cause apparent changes in the mass of the

object. The method is also subject to the

normal ambiguities associated with mass measurement. Generally, the method is limited

by the availability of equipment and handling

problems associated with the object.

The largest number of volume measurements

are associated with determining the amount

of liquid which is "contained" in, or can be

"delivered" from, a variety of appropriate

vessels, i.e., pipets, burets, flasks, metal

containers or capacity standards, process

tanks, etc. When the container design is

such that it can be weighed in the filled

condition, the containment volume is determined by gravimetric methods. The container

is first weighed in an empty condition, then

filled to an appropriate index with a liquid

of known density and reweighed. The volume

of the liquid, determined from the definition of density, is assumed to be the volume

of the container. The method is subject to

all of the ambiguities associated with mass

and volume measurements, as described above.

For "delivered" volume, there is an ambiguity associated with the tendency of the liquid to cling to the walls of the container

during drainage. In this case, the con- tainer is filled and drained for a specific

time interval before the first weighing.

With proper attention to the ambiguities, one can establish the volumes of large con- tainers by transfer methods, e.g., a repetitive operation consisting of filling a con- tainer of known volume to an appropriate

index, and emptying it into the larger

container.

2.1.3 Density

Density is defined as mass per unit volume. It is not a measurement unit in the

same sense as mass and volume. It is a unit

generally used to characterize a material,

be it gas, liquid or solid. In certain

cases density may be a measure of mass distribution within the boundaries of the en- closed volume, e.g. certain gas and gas

mixtures, certain pure liquids, and certain

solids. In many cases density is merely a useful characteristic of an object.

Because of large numbers of ambiguities

which are involved in both mass measurement,

and direct measurement of volume using a length metric, the most precise density work

has been limited to the characterization of

specific reference materials: water, because

of its prominence in the establishment of

the metric unit of mass and its availability

as a reference material; mercury, for use in

pressure measurement; and most recently,

single crystal silicon. Density work with

regard to a reference material has an additional complexity over and above those asso- ciated with measurement: that of the

uniformity of the reference material over

time and as obtained from various sources.

2.2 Basic Technical Infrastructure

Mass

The accepted standard mass unit is the mass of the International Prototype Kilogram, a pi ati num-i ridium cylinder of height

very nearly equal to its diameter. The mass

of this object is exactly one kilogram by

definition. There are no environmental res- trictions associated with the definition.

In the comparison of the International Prototype Kilogram with its replicas, the am- biguities mentioned above are not large,

provided that sufficient time is allowed

for the surfaces to come into equilibrium

with the environment since the objects are made from the same material with nearly the

same surface finish.

The acceptance of the International

Prototype Kilogram as the standard of mass

did not end the confusion associated with

mass, weight and force. In 1901, the 3rd

General Conference on Weights and Measures

(CGPM) declared:

1) "The kilogram is the unit of mass;

it is equal to the mass of the

International Prototype Kilogram;"

2) "The word weight denotes a quantity

of the same nature as force; the

weight of a body is the product of

its mass and the acceleration due

to gravity."

This second statement, a deviation from the

general policy of the CGPM of defining only

units but not quantities, demonstrates the

wisdom of this policy.

The 11th CGPM, in 1960, established the

derived unit for force, the Newton, which is

defined as the product of mass and acceleration. This action, in essence, relegates

the word "weight" to mean an object which

has a mass property of interest. In reality

the words weight, mass, and force are still

syntactically confused. The degree to which

the populace, as well as those directly interested in mass and force measurements,

accept the Newton remains to be seen.

In this country, the most common metrics

for mass measurement are the avoirdupois

pound, with a growing use of decimal subdivisions, and the kilogram, with the usual

subdivisions. Traditional subdivisions of

the pound are required by legislation to be

used in some areas, e.g., the Troy pound and ounce are used in precious metals trade;

grains, in coinage. All now have been

defined, directly or indirectly, relative to
the kilogram. There are no inconsistencies

between the various metrics.

In determining the mass of an unknown

object, the metric can be introduced in one

of two ways; by direct comparison with an appropriate summation of mass standards,

relying on the instrument indicating system

to subdivide the smallest practical standard, or by direct measurement using a device which has been designed to indicate

either mass units directly or some mass re- lated quantity of interest, or both, e.g.

the grocery store pricing scale. The choice

of method depends upon the end usage of the

measurement results.

In the comparative mode, the constancy of

the metric is determined by the available

summation of mass standards. The uncertainty of the result is a function of the uncertainty of the mass value assigned to the

standards, the precision of the instrument,

the care exercised in making the measurement, and the attention given to significant

ambiguities. In the direct reading mode,

the constancy of the metric is assigned to the instrument. The uncertainty of the re- sult is then a function of both the long

term stability of the instrument and its

precision, as well as the uncertainty of the mass scale as embodied in the instrument.

The instrument design usually includes some compensation for significant ambiguities.

It remains for the user, however, to ascertain that such treatment is indeed appropriate for his particular measurement. In practically all cases, commercially available instruments are designed to be used as direct reading devices. Most instruments,

however, can be used in either mode of

operation either as is, or with minor

alterations, if the instrument indicating system has not been arbitrarily

rounded.

The most confusing technical problem

concerns the basis for stating mass values.

In addition to confusion between mass, weight and force as mentioned above, there

are at least three "mass scales" in common

use. To understand the origin of these

scales, consider the case in which a stan- dard of known mass is compared with two

"unknowns," one made from the same material

as the standard, one made from a different

material. In comparing the like materials

of essentially equal mass, the

buoyant effect becomes a second order

correction, and the value transferred to the unknown is on the same basis as the

value assigned to the standards. Where

the materials are different, the buoyant

effect must be reconciled in some manner. The practice was started long ago where

the value assigned to the unknown was

called "apparent mass," and was assigned

on the basis of the observed differences.

Later, the precision of the "apparent

mass" scale was preserved by normalizing

the data to obtain the value one would

expect if the unknown had been compared

with a hypothetic standard of stated

density in a specific environment. The

oldest "apparent mass" scale used in this

country is based on a standard of

7.8 g/cnr at 0°C and an air density of

1.2 mg/cm . The newest scale, originating

in Europe and Japan, is based on a standard of density 8.0 g/cm^at 20°C and an air density of 1.2 mg/cm3

. The systematic difference between the two scales is

observable on many instruments. Finally,

there is the "Newtonian" mass scale, e.g.

"true mass" or "mass in vaccuo," for which

the International Prototype Kilogram is

the defining artifact.

Volume

The founders of the metric system, in an attempt to establish a reproducible mass

unit, defined a mass unit, the gram, to be

the mass of one cubic centimeter of pure

water at the temperature of maximum density.

On the basis of this definition, and the

newly established length unit, the meter,

the Kilogram of the Archives was constructed using arbitrary mass units as embodied

in the Pile of Charlemagne [14]. Using

Archimedes' Principle, and objects with

measured displacement volumes in terms of

the meter, the summation of arbitrary mass

units which would be equivalent to one kilogram was established. It then remained

to construct and adjust the newly established kilogram to be equal in mass to the

appropriate summation of arbitrary mass

units. This work was a substantial scientific effort, with careful attention to the ambiguity associated with the buoyant

effect of the air. There was no way to check the realization however, since the

available platinum-i ridium alloy used in

the construction of the Kilogram of the

Archives was too porous to permit a hydrostatic determination of the displacement volume. It was generally accepted,

however, that the kilogram was equivalent

in mass to that of one cubic decimeter of

water at its maximum density point [15].

A later group of pi ati num-i ridium kilograms, from which the International Prototype Kilogram was selected on the basis of

being most nearly identical in mass to the

Kilogram of the Archives, was of sufficient

quality to permit hydrostatic determination

of displacement volume. It was then evident

that the intended realization was not

achieved. In 1903, the unit of volume was
defined by the third CGPM as follows:

"The unit of volume, for determinations of

high precision, is the volume occupied by a mass of one kilogram of pure water, at its

maximum density and under normal atmospheric

pressure; this volume is termed the litre. "[1 No reference is made to the unit of length.

Careful measurements had shown that the mass

of one cubic decimeter of water at its maxi- mum density point differs from the mass of

the kilogram by 27 milligrams. As measurement precision has increased, the confusion

between the cubic centimeter and the

milliliter has done likewise.

The eleventh CGPM in 1960 requested a re- solution of this controversy which subsequently occurred at the twelfth CGPM in

which the definition given in 1901 was abrogated, the recommendation made "that the name 'liter' should not be employed to give

the results of high accuracy volume measurements, but that high accuracy measurements

be expressed in the SI units, i.e., in cubic

meters or cubic decimeters."

For liquid measure, the most common metrics are cubic decimeter (usually called

liter in spite of the above recommendation)

and the U.S. gallon, which has a defined re- lationship to the SI length unit.

Density

During the era encompassing the third

CGPM, about 1900, the thermal coefficient of

expansion of normal (to be defined) water

was measured [17,18]; and in 1937, Tilton

and Taylor at NBS [19] published tables (expressed in grams per milliliter) of the re- lative densities of water as a function of

temperature from a formula they constructed

to fit the early data. Around 1910, BIPM

[20,21,22] had measured the true volume (in

cubic centimeters) of a milliliter by hydrostatical ly weighing objects of directly

measured volumes in normal water. "Normal"

water is now defined as that having a "normal" or "average" isotopic abundance

ratio.

Modern workers [23,24] have shown that

the isotopic abundance ratio in samples of

water drawn from various locations on earth

may vary enough to result in density differences of as much as 5 or more parts per

million. Without knowledge of the isotopic

abundance ratio, we are left with an uncertainty of this amount in the accepted

density of a particular sample of water.

Additionally, there is an even larger source

of uncertainty. The vapor pressures of the

various isotopic forms of water are significantly different [25], so that distillation

to remove impurities or boiling to eliminate

dissolved gasses can further upset the isotopic abundance ratio from its "normal"

value. Density differences as great as 20

ppm have been found [26] between the first

and last fractions of a distillation.

Uncertainties in the density of "pure"

or "normal" water, still under study, limit

its use as a reference material in high ac- curacy measurements. Water, however, is an adequate reference material for a wide variety of measurement activities. The most

recent fit of the original data has been

done by Wagenbreth and Blanke [27]. In this

work the data has been adjusted to the In- ternational Practical Temperature Scale of

1968 (IPTS-68), and the density values, ex- pressed in SI units (kilograms per cubic

meter) are tabulated for the temperature

range 0° to 40°. Density values, as given

in this work, are used at NBS for all volume

measurements in which water is used. In some cases, the values can be adjusted for use with normal tap water.

The problem of uniformity of the refer- ence fluid was handled in a different way by

Cooke in his work with mercury. In essence,

the final results apply to a large quantity

of mercury obtained by mixing samples from

a variety of sources. The mix was then subdivided, with smaller quantities being

furnished to national laboratories interested

in high accuracy pressure measurements.

Following the demonstrated ability to compare densities of silicon crystals at the

1 X 10" level [28], Bowman, Schoonover, and

Carroll [29] have established the density of

single crystal silicon artifacts with

measurement uncertainty on the order of 1 ppm.

In this work, the volume of a group of steel

spheres was determined by interferometric

measurement. Spheres were selected because

manufacturing processes have now been perfected to the point that nearly perfect geometry is readily obtained. Working with the

buoyant forces in a fluid of arbitrary density, one can determine the volume of other

objects relative to the measured volume of

the spheres, the result being independent of

the mass unit. This work suggests that the

natural density of single crystal silicon

may be more constant than obtainable with

water in any form. Artifacts of known density in combination with mass measurements

and Archimedes' Principle, can be used to characterize either fluids of interest or other objects. Crystal samples have been

furnished to other laboratories, including

BIPM.

In contrast to the high technology work

briefly described above, most practical density measurements are made to characterize a wide variety of fluids, again a problem of

interest since man discovered the pleasures

of alcohol. The resulting measurement system, revised and improved over the centu11
ries, is a simple, practical solution to a very complex problem. This complexity

arises from the fact that where solutions

are involved, volumes are not additive.

Further, the changes in density of the solution with temperature cannot generally be

predicted from the characteristics of the

solution components.

Based on Archimedes' Principle, a hydrometer floats in the solution at a level

where the buoyant force acting on the submerged portion of the instrument balances

the gravitational force. The sensitivity

of the instrument depends on the ratio of

the stem cross section area to the submerged

volume. A reading scale in the stem can be

graduated in any units which are related to the density of the fluid. Further, by

selecting the density of some arbitrary

fluid at a particular temperature as unity,

the instrument is not dependent on any

system of measurement units. Since distilled

water is a widely used dilutant, it is the

basis for a variety of "density" scales.

Figure 4 illustrates some of the more common metrics currently in use. The starting point for hydrometer calibration is the selection and preparation of the

reference fluids. In the case of simple

solutions, for example, a series of solutions of known dilution are prepared from

pure materials. For more complex fluids,

density is determined by weighing using

weighted glass plummets of known displacement volume, or picnometers of known con- tainment volume. These solutions are used

to establish appropriate scales on reference

hydrometers. Corrections for temperature

effects are essential. Sets of reference

hydrometers for the common metrics are maintained at the various national laboratories. The reference standards are used to calibrate "master" hydrometers for manufacturers and certain classes of users. The

"master" hydrometers are an essential part

of the manufacturing process. It is not generally possible to control the physical

dimensions of the hydrometer to a degree

commensurate with the sensitivity of the

instrument. For each precision instrument,

the scale must be established relative to an appropriate "master" hydrometer as one step

in the manufacturing process. The finished

instrument may then be checked against

another "master" hydrometer, either by the

manufacturer or the user, or it may be

submitted to a national laboratory for calibration relative to the appropriate

reference standard.

Recent developments include a method to establish reference hydrometers without

using reference fluids, provided that the

surface tensions and thermal characteristics

of the fluid are well known, and provided

that the desired scale is defined relative

to the SI unit for density. [30] The most

important development is the availability of

a new type of instrumentation for density

measurement based on the inertial properties

of mass, described in Section 2.2.2.1.

2.2.1 Documentary Standards System

We define documentary standards to include all documents which are formulated

for the purpose of providing solutions to

constantly reoccurring routine problems. This

includes recommendations, test methods and

procedures, and specifications, both

hardware and performance. All standards are,

in a sense, after-the-fact documents, and as such reflect an acceptable consensus decision

with respect to some particular problem.

Standards provide a degree of order which in

many cases produce economic savings to both

the producer and the user. Perhaps more important, standards provide a means to

address the legal problems associated

with supply and demand, e.g. the

specific desires of the customer, the

limits of control by the regulator,

the limits of guarantee or warrantee

by the producer, and some form of proof

that "due care" was exercised to comply

with appropriate restraints.

2.2.1.1 Standardization Institutions

The first of these is the apparatus set

up by the Treaty of the Metre of 1875. This

structure has two levels, diplomatic and

technical. Nations who are signatories of

the Convention of the Metre are represented

on the General Conference for Weights and

Measures (CGPM). This body, composed of na- tional delegates, elects the International

Committee for Weights and Measures (CIPM)

and formalizes the international adoption of

recommendations. These recommendations in essence promote uniformity in communications

by defining the various base units, in this case the kilogram and the meter, and the

various derived units.

It should be emphasized that the organization established by the Treaty of the

Metre is concerned only with the realization of the units. The utilization of the

units, so defined, is left to others.

International Bureau of Weights and Measures (BIPM) is the laboratory arm of CIPM.

From its location just outside of Paris, it serves as secretariat to the advisory

committees, maintains the prototype kilogram and periodically intercompares the

National Prototype Kilograms belonging to the member nations.

12
Figure 4 PRACTICAL HYDROMETER SCALES

COMPARISON OF VALUES

— Hydrometer Scales. ->-

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m

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^ If $ IP

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J- Il

*C/OS 3t>£. L/7>OS</S.

aire*?. C

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13
A second international treaty organization is the International Organization for

Legal Metrology (OIML). Its objectives are:

(1) to determine the general principles of

legal metrology;

(2) to establish model draft laws and regulations for scientific and measuring

instruments and their use; and

(3) to determine necessary and adequate

characteristics and standards to which

measuring instruments must conform in

order for them to be approved by member

states and for their use to be recom- mended internationally.

Actions of the Conference on Legal Metrology are in the form of recommendations and are not legally binding, but member nations

are morally obliged to implement decisions

of the Conference as far as possible [31].

A nontreaty international standards organization of importance is the International

Organization for Standardization (ISO). The

American National Standards Institute (ANSI)

is the United States member of the International Organization for Standardization,

which now consists of the national standards

bodies of 52 countries. The United States'

viewpoints to be presented in the technical

work of the ISO are developed either through

the interested sectional committee or through a competent committee of another or- ganization or, if there are none of these

available, through a committee specially or- ganized as a USA Advisory Committee for the

ISO Technical Committee.

The work of the ISO technical committees

results eventually in ISO Recommendations

which may be embodied in the national standards of the ISO's Member-Bodies. ISO re- commendations, like all voluntary standards,

may be in the form of either detailed "how

to" specifications or overall performance

specifications, e.g., "standard" test for

determining the density of crude oil or a listing of agreed upon ranges for hydrometers.

ANSI and the American Society for Testing

and Materials are the two largest of over

500 organizations in the United States who

consider the preparation of standards to be

a major or important part of their reasons for being [32]. The field of expertise

found in both the ASTM and ANSI type of or- ganization is best described by ASTM's

managing director: "Actually, the Society

has only one area of expertise and that is a full knowledge of management systems for the

development of consensus standards" [33]. A great deal of care is taken to ensure user participation in any committee to avoid

antitrust action.

Voluntary standards organizations work

through a committee structure whose membership is composed of representatives of users

united in a common endeavor, or the manufacturers and users of a product or technique.

In the latter case, it is generally true

that manufacturers' input is very strong unless the area of interest concerns a large

number of users. The Federal Government within its procurement process generates specifications

which become, because of the size of the

government market, de facto national standards. Other Federal Government agencies,

such as the Department of Defense and the

various regulatory agencies produce standards which impact all aspects of

measurement.

State and local governments also produce

standards of varying degrees of impact. By

far the most important of these, within the

context of this document, are the weights

and measures laws which are currently issued

by 775 separate jurisdictions. While the

legal responsibility is at the state level,

national coordination is obtained through

the National Conference of Weights and Measures, sponsored by NBS through the Office

of Weights and Measures.

2.2.1.2 Survey of Documentary Standards

CGPM resolutions define the metrics for mass and length, and the terminology for the

SI base and derived measurement units. Resolutions are universally adopted by the 93

signatories of the Conventions. Efforts to provide access to these measurement units

generate a literature base associated with

the "how to" of measurement, e.g., instrumentation design and development, constancy

of the unit, and the performance of the

measurement process over time and in the

various environments in which measurements

must be made. This literature base is a ma- jor resource for measurement application.

The community which is concerned with the

"how to" of measurement is not generally re- stricted by either proprietary or legal

limitations.

The application of the "how to" of

measurement to resolve specific measurement

problems generates standards which can be

categorized according to the nature of the

specific problem. For routine problems with

wide application, e.g., instrument performance specifications and the adjustment tolerances for different classes of mass standards, or of interest to large sections of

the populace, e.g., weights and measures activities, the resulting standards are readily accessible to all who have interest.

Ease of access, in turn, results in such

standards inadvertently becoming a part of

the "how to" literature base. The "how to"

14
of measurement will be discussed further in

section 2.2.3.

The largest number of standards relating

to application are the "in house" standards

of the producers of goods and services. In order to limit liability with respect to contract compliance, warrantee or guarantee,

such standards are not widely circulated.

In many cases there is a concerted effort to protect the proprietary nature of these

standards within a given organization, with

circulation based on the "need to know."

While standards of this type are the basis

for eventual consensus standards, the existence of a consensus standard does not preempt the use of the "in house" standard.

Product performance, established and maintained by "in house" standards, may be defended in a legal sense on the basis of consensus standards.

The basic differences between the OIML

and the voluntary and government standards

are related to the means of deciding what

constitutes "due care" in a legal sense. OIML is an effort to define "due care" at a national level through the control of mea- surement detail. OIML recommendations pertaining to artifacts and measuring devices

specify the placement of a metro! ogical control mark upon the article in question.

That is every article of that type must

bear the "mark." Obtaining the "mark" for

a product requires adherence to the specifications of the instrument or artifact engineering design contained in the pertinent

recommendations.

For example, a case in point is that of a U.S. manufacturer of weights attempting to market his product in a nation subscribing

to OIML recommendations [34]. A prototype

approval was required before any weights

could be sold. Submission of a typical set

of weights resulted in rejection based upon

the dimensions of the weights rather than

on the suitability of the weights for the

specific application.

Further, the 59th National Conference of

Weights and Measures passed a resolution

pertaining to OIML in which it defined its

view of the "moral obligation" involved in

the treaty. That resolution specified

that the NCWM was not morally obligated to implement any OIML recommendation, i.e., a model weights and measures law, which had

not been approved by the NCWM after review

and acceptance and only then if the U.S. had

cast an affirmative vote for the model regulation in the International Conference of

Legal Metrology.

The U.S. Advisory Panel who reviewed the

first 19 recommendations found 18 technically unacceptable. The ultimate impact on

U.S. industry is a cause of concern due to

the potential, and to a degree existing, use

as nontariff barriers to trade.

Voluntary standards organizations, in es- sence, establish "due care" at the producer

or the producer/user level. By mutual consent, voluntary standards dealing with materials are generated by the American Society

for Testing and Materials (ASTM), and those

dealing with devices by the American National Standards Institute (ANSI). There is

close cooperation between the two institutions and their standards are similar in

nature. ANSI has an additional role re- lating to ISO. ANSI represents the United

States' views in the international voluntary

standards effort. Both ANSI and ASTM standards are subject to periodic review.

The role of voluntary standards in

American industry is complex and generally

not well understood. Voluntary standards

are "how to" documents for a variety of

specific tasks. The standards are essentially defense mechanisms. In most cases, the issuance of a standard is contingent

on a unanimous affirmative vote by the

reviewing body. The time interval between concept and approval is on the order

of 5 years, with mandatory review intervals of 3 to 5 years. After issuance there

is another time interval, also measured in

years, during which the standard is implemented by the various users. As a consequence, voluntary standards serve stability

rather than viability. Nonetheless, the

collections of voluntary standards are used

by many as authoritative "how to" standards

for measurement.

Professional societies, such as the Society of Automotive Engineers, the American

Society of Mechanical Engineers, the Institute for Nuclear Materials Management acting

through ANSI, develop and issue standards as do some 360 trade associations. There are

at least 20,000 such standards, accessible

via NBS SP 329, "An Index of U.S. Voluntary

Engineering Standards." An ASTM subcommittee

on balances has reviewed all of the ASTM

specifications to identify those in which

mass measurement was limiting. As expected,

in an excess of 20 volumes of specifications, there were no mass measurement re- quirements which could not be satisfied with

available instruments and procedures. In many cases, however, the specifications did

not reflect a knowledge of the convenience

and economy associated with modern methods

and instruments.

Federal Standards, issued by the General

Services Administration for use by the government in the purchase of consumer goods,

represent a different approach to the "due

care" problem. These standards represent an arbitrated resolution of differences between

15
user requirements and vendor capabilities,

with specific attention to the factors used

to differentiate between an acceptable and a nonacceptable product, i.e., carefully

address the legal aspects of "due care."

These standards are subject to periodic re- view. There are approximately 28 such standards relating to mass, volume and density.

In the case of volumetric glassware, the

size of the government market relative to the total market is such that these specifications are essentially industry specifications, with obvious benefits to the

nongovernment user. The Department of Defense Standards relating to the procurement of weapons systems

have an important role in American technology. Weapons procurement involves high technology design, development and production,

usually where there is no precedent for design, or where performance specifications

are far more stringent than those associated

with normal commercial products. Currently

such procurement is based on a vendor res- ponsibility concept. In this framework, the

procurement procedures must address the

problem of what constitutes "due care" on the part of the vendor in the course of

carrying out the contract.

The resulting system is set up under the

basic documents which affect all areas of

measurement:

MIL-Q-9858A "Quality Program Requirements"

MIL-C-45662A "Calibration System Requirements"

MIL-I-45208A "Inspection System Requirements"

DSAM 451553 "Evaluation of a Contractor's

Inspection System."

The implementation of these documents has

resulted in the establishment of a system

for measurement control, the operation of

which is a contractual requirement, and the

inspection of which is carried out by the

contract administrator. In excess of 65% of

the total calibration activity of NBS directly supports the resulting systems. It should be emphasized that the system is, in

view of the procuring agency, a minimal effort necessary to production of acceptable

goods, i.e., a definition of "due care." No attempt is made to resolve problems where

the required measurement effort has no relation to the quality of the product or where

the output of the system is inadequate for

the task at hand.

Weights and measures activities, a state,

and to some degree a local, function, are basically concerned with the legality of mass, volume and density measurement within

the context of trade and the enforcement of

regulatory requirements originating at the

state or local level. The principal universal documentary standard is Handbook 44,

"Specifications, Tolerances and Other Technical Requirements for Commercial Weighing

and Measuring Devices." This loose leaf

style handbook, periodically revised, is

technically the output of the National Conference of Weights and Measures (NCWM). The

Office of Weights and Measures of NBS acts

as the Secretariat of the NCWM, providing

guidance and coordinating various activities. HB44 Has been adopted by all 50

states and incorporated into their weights

and measures laws. In addition, 28 states

have chosen to adopt uniform weights and measures laws following a model law prepared

by NBS and approved by NCWM.

2.2.2 Instrumentation Systems

Broadly speaking, the instruments for

measurement of mass, volume and density con- sist of a wide variety of measuring devices,

artifacts, and procedures. Drastic changes

in all of these categories have occurred over the past few decades. The precision

balance industry has changed from the isolation of a tightly controlled craft to a high

production, high technology industry with

worldwide sales and service. A few foreign

firms satisfy essentially all of the market

demands. These same firms, concentrating on the problem of making good measurements

rapidly and conveniently, have had an impact, on all types of weighing devices. The market for weight sets has essentially disappeared, with only one small company in this

country devoting part of its efforts to supplying conventional weight sets, and perhaps

a few supplying special sets to weights and measures officials. The use of volumetric

glassware, particularly in clinical laboratories, has been replaced by a variety of

completely automated test equipment. New instrumentation has been developed for

determining densities of fluids. Weighings

which were previously done in the market are

now being done with weighing devices incorporated in complete packaging systems. Procedures, which were carefully designed to maximize the performance of the older instruments, are no longer applicable.

The above changes have been made

economically feasible by concentrating the

design and manufacturing effort on the areas

in which there is a large market, i.e., from

a few grams to a few kilograms. There is

only one firm in this country, and perhaps

in the world, that markets a 30kg capacity

instrument of other than traditional design.

Only two companies in the world offer custom

16
built kilogram balances with performance in

the microgram range. One in this country

offers an instrument based on NBS design for

about $75 000, and one in Japan, for about

$125 000. Equal arm balances with 5 000 1

b

capacity have been custom built; they are

not available commercially. Most large

capacity weighing devices are designed for

use as commercial weighing devices, i.e., in

accordance with Handbook 44, or other appropriate specification. The nature of the industry is such that a large amount of capital investment is required to design, develop, market, and service a new instrument.

As a consequence, manufacturers are very

reluctant to supply special equipment to

limited markets. Performance claims are generally limited to that obtainable by

simplified procedure in relatively poor

environments.

Two other recent developments have had a large influence on the instrumentation system: the availability of stainless steel for

use in mass standards, and the ability to characterize an individual measurement

process, and groups of similar processes. The

stability of stainless steel weights, e.g.,

constancy of mass values, is superior to brass in any form, and perhaps even superior

to the platinum-iridium alloy of the prototype kilograms. Careful material control

associated with the "built in" weights is

important to the success of modern instruments. Computer analysis of large sets of

data provides quantitative parameters

descriptive of actual instrument performance

which in turn guides the development of

equipment and procedures.

The most important development of the

last decade, generally made possible by

electronic advances, is a change in the way

in which the instrument indication is determined. Traditionally, changes in the angular position of the beam, as the balance is

subjected to different "pan" loads, have

been used to indicate differences in mass.

In increasing numbers of instruments, the

beam is driven to a prescribed "null" position by applying an auxiliary force to the

beam through a servo system. The current in

the "feedback" loop of the servo is then a measure of the mass difference. There are a number of advantages: the use of flexural

elements instead of knife edges, rapid operation, and a signal which can be read

di rectly by a computer.

2.2.2.1 Measurement Tools and Techniques

Measurement tools and techniques are largely determined by the way in which the

result is to be used. Two sources of ambiguity must be considered, the response of

the instrument to changes in environment and

the ambiguities associated with the concept.

The sophistication and, to a large degree,

the cost of the instrument depends on the

degree to which the manufacturer has minimized these effects by design. Depending on the materials to be weighed, ambiguities

associated with the concept must be considered at the part in 5 000 to 10 000 level.

Beyond this point, the instrument indication

may or may not be an appropriate measure of

the mass of the object or material being

weighed. Most weighing instruments are intended to be used as direct reading devices, and as such, are adequate for all

requirements where the accepted uncertainty

of the result is determined by factors which

are not related to the measurement process,

e.g., the grocery store pricing scales.

This creates a competitive market in which

speed, convenience, and maintenance costs,

and perhaps certain regulatory requirements,

are important factors.

As the limits for acceptable uncertainty

approach the magnitude of the ambiguities

associated with the process, one must either

restrict the magnitude of the process ambiguities, e.g., impose environmental controls

and limit the class of objects to be

weighed, or one must adopt more sophisticated procedures and methods for data analysis.

Specifying one particular weight material,

for example, extends the speed and convenience of the pricing scale into the calibration laboratory which is concerned only with

the maintenance of the unit. Such action,

however, does not necessarily account for

ambiguities in the assignment of mass values

to other materials. With few exceptions,

everyone must use commercially available

equipment for mass measurement. Therefore,

one must resort to procedures and techniques

to make adequate measurements for requirements which are beyond the performance

claims of the manufacturer.

The instrument indication is in essence

an amplification of the mass difference

between the object in question and a "tare" setting. The prerequisite for changing the

mode of operation of the instrument from a direct reading mode to a comparative mode

is that the indicating system not be

intentionally rounded to obscure randomlike variability as the sensitivity is

increased.

In a comparative mode of operation, with

appropriate procedures and attention to environmental conditions, one can achieve

the maximum instrument performance. The

convenience of direct reading, however, is generally sacrificed. In a comparative

mode, the constancy of the unit is shifted

from the instrument to a stable artifact.

17
The significant ambiguities are accounted

for by attention to environmental factors,

and by treating the ambiguities associated

with the concept in the data analysis.

Where requirements are stringent, it may be

necessary to use supplementary measurement

data to determine the displacement volumes

of the objects of interest, and to determine

the density of the air in the vicinity of

the instrument.

Thje most readily identifiable artifacts

in mass measurement are the weights or weight sets which provide local access to the measurement unit. In those nations

which are members of the Treaty of the

Metre, a national laboratory has the task of

transferring the unit as embodied in the

appropriate prototype kilogram to a more

practical weight material. This work, in

essence, substantially reduces the magnitude

of the ambiguities associated with the con- cept in providing the nation with access to the unit. Errors in the initial transfer,

however, become systematic offsets of the

practical mass scales of the various nations.

There are in effect two systems for the

dissemination of the unit with reference to the practical artifact standard. Starting

with an artifact with defined value, an equal arm balance, and a mass of material

slightly in excess of that of the artifact,

one can carefully remove material from the

"unknown", until a comparison indicates a "null" condition. At this point, one could

declare the mass of the two objects to be

"identical." As one increases the sensitivity of the balance, at some point it becomes

impractical to make further adjustments.

The residual difference is then determined

from the balance indicating scale. One can

now announce the results of the work in one

of two ways: the mass of the adjusted object

does not differ from the defined mass of the

standard in excess of some appropriate

amount, e.g., difference expressed as a percentage error; or, the mass of the object

relative to the mass of the standard is a particular value, usually expressed as a nominal value plus a correction, the sum of

which is the assigned mass of the object.

For example, the CGPM, in distributing the

prototype kilogram, announced that maximum

difference in mass between the prototypes

and the defining artifact did not exceed

1 mg. The reports of calibration from BIPM

in contrast, state mass values relative to

the defining artifact with uncertainties on the order of a few micrograms. The relative

importance of these two points of view, one emphasizing the closeness to the nominal

value and the other value relative to the defined value, has changed drastically over the

last few decades.

For centuries, precision weighings were made by comparing the mass of the object of

interest to the mass of a summation of known

weights with an equal arm balance. The

necessary weight sets were provided through

a hierarchy structure of mass standards. The

adjustment problem was solved by using two

piece weights, the weight body with an appropriate cavity, and a cover or seal for

that cavity. In the adjustment process,

small pieces of material were added to achieve equality with the known standard

according to prescribed limits of adjustment,

and the cavity was sealed. The mark on the

seal was, and in some cases still is, a symbol which verified the authenticity of

the adjustments. Such weights were also,

and still are, used to verify the perfor- mance of direct reading commercial weighing

devices. The structure was simple, and

easily understood—to make a better measure- ment all one needed was a set of weights

from a higher level in the hierarchy, e.g.,

weights which had been adjusted closer to

the prescribed nominal value.

Modern weighing devices remove the choice

of weight sets from the user. As before,

the user assembles an appropriate summation

of weights to obtain an "on scale" condition

using the appropriate controls on the instrument and then relies on the indication

to subdivide the mass of the smallest internal weight. The instrument manufacturer has

taken the responsibility for the construction and adjustment of the reference

standards. The weight materials are chosen

on the basis of stability. Using techniques

such as electropolishing, weight adjustments

can be made on a production basis with deviations from nominal essentially limited only

by the uncertainty of the values assigned to appropriate reference standards. The instrument case provides clean, dust-free, and

essentially nonaccessible storage. In at

least one case, instrument assembly is done

in a "clean room" environment. The design

philosophy is in essence to remove the res- ponsibility for the detail measurement procedures from the user with a well engineered

instrument. The instrument cost is considerably more than a traditional equal arm bal- ance and a set of weights, however, in terms

of cost per measurement, the traditional

methods are obsolete.

The change in emphasis from the closeness

of adjustment to actual value is not without

problems. Everyone whose concept of mass measurement was formulated before the last

decade, including the scientific community,

views mass measurement as a hierarchy of mass standards. The most prevalent manner

of expressing measurement error is relative

error, e.g. in error so many parts per

18
million or percentage. While this may be a convenient or valid way to express error in some cases, the error in mass measurement

is not quantity proportional. A part in a billion measurements can be made at the

kilogram level, but not at the gram or milligram level. Further, long standing regulations and specifications which are the

basis for a number of inspection systems

cannot cope with instruments which are

"better" than the available hierarchy

standards.

With one exception, volume and density

measurement is essentially mass measurement

instrumentation applied to a different set

of artifacts, e.g. a wide variety of volumetric containers, hydrostatic weighings to determine displacement volumes or fluid density, picnometers, etc. One characteristic

of interest is the coefficient of expansion

of fluids over a rather wide range of tem- peratures. Traditionally, a picnometer (a

special glass container of known contained

volume) is filled and sealed in a temperature controlled bath. [35] After sealing,

the picnometer is cooled to a temperature

compatible with the weighing device. From

the weighing data and the characteristics

of the picnometer, one can determine the

temperature-density characteristics of the

fluid. The method is tedious and time consuming. A very successful instrument is now available which reduces the task to simple

routine. The instrument, using the inertial

properties of mass, relates the response of

a quartz tube, filled with fluid at a specified temperature, to an oscillating force

field, to the density of the fluid. The instrument, in essence a "density comparator,"

can be used over a range of temperature.

When well characterized fluids are used for

calibration, near state-of-the-art precision

can be obtained and density determination

can be made in a few minutes.

From the previous discussions in this

section, it should be clear that a wide

variety of techniques for taking and

analyzing the data are used. The degree of

complexity of these techniques and procedures is directly related to the manner

in which the result is to be used. One

such technique, now called Measurement

Assurance Programs, was developed in the mass measurement area. [36] This technique

addresses the problem of how one obtains

the assurance that the measurement results

are valid when forced to utilize the maximum capabilities of a particular measure- ment process. Using redundancy of

measurement, "check standards", i.e.

objects similar in nature to those which

are measured routinely but which remain

as a part of the process, and statistical

19

analysis, one concentrates on characterizing a particular measurement process.

Performance indices are developed which

reflect the influence of major perturbations on the process, and which are valid

prediction limits for uncertainty of mea- surement results over the range of variables for a given process. The programs, once established, provide a continuous

monitoring of process performance. The

validity of each measurement is checked

relative to past process performance.

2.2.2.2 The Instrumentation Industry

Weighing instrumentation can be

considered in two classes; Laboratory

Precision Balances and Commercial Scales

and Balances. The nature of the two industries is significantly different.

The laboratory precision balance industry

is primarily foreign, centered in Europe and

Japan. The individual companies, while few

in number, are large, some with worldwide

sales and service organizations. Total

sales figures are carefully concealed,

however, it is estimated that one European

firm has captured approximately 70% of the

world market. Marketing in the United

States is through wholly-owned subsidiaries, or through agreements with American firms.

Many of the balances in the NBS Mass Laboratory, and all of the balances furnished to the State Laboratories, with the exception

of the 30 Kg balances, are foreign made.

The restrictive nature of the various states

weights and measures regulation has generally blocked these firms from the Commercial

Scales and Balances field.

The American industry devoted to laboratory precision balances is a group of small

companies. The equipment is usually marketed through laboratory supply houses or manufacturers representatives. Few have

nationwide sales and service organizations.

Most, however, operate short courses in

service for journeymen who operate general

balance and scale repair organizations. The

industry has been somewhat protected by

various "Buy American" clauses which are used occasionally in certain government

contracts.

In contrast, the Commercial Scales and

Balances industry in this country is large,

with a number of firms having nationwide and

international sales and service organizations. In general, the industry has been

conservative and very conscious of the

limitations associated with the various

weights and measures regulations. A wide

variety of equipment is available for both

single weighings and large complex systems,

e.g., packing systems, counting systems,
etc. Pressures from many sources, including marketing, prepackaging, and to a certain extent the foreign precision

balance industry, seem to have generated

some recent innovations evident in most

grocery markets.

Volumetric glassware is produced by large

firms who generally market by the case to

large users and various scientific apparatus supply houses. Special apparatus for

which there is no large market is produced

by small companies. The grade of the glassware is established by compliance with specification requirements, some of which are performance specifications and some of which

are detail specifications. The size of the

market is established in part by the breakage rate in use and by the cost of cleaning

after use. Throw-away plastic apparatus is

a significant competitor.

Hydrometers are generally made by small

companies, usually in conjunction with

liquid-in-glass thermometers. Again the

grade is established by specification compliance, and as with all glassware,

breakage is a factor which tends to support

the industry. Hydrometers are not usually

general purpose instruments, but related to

specific uses, e.g., the tax structure for

alcoholic beverages, the petroleum industry,

the sugar industry, etc. As a consequence,

the market is generally governed by specific industry actions.

Metal volumetric containers, such as used

for testing liquid and gas metering devices

and for calibrating process tanks, are produced by one or two small companies. Most

of the market undoubtedly consists of re- placing damaged devices. Large companies

which produced such items in the past have now either sold that portion of the business

or just stopped production. Again there is an interface with regulatory requirements

which to some extent dictates the equipment

detai 1 s. Table 2 provides an estimate of the size

of the American industrial effort relating

to mass, volume, and density measurements as compared to the larger category Engineering

and Scientific Instruments (SIC 3811).

Table 3 provides an estimate of the num- ber of devices in use for commercial weighing

and an approximate cost per device. Currently available precision weighing devices with

capacities from a few grams to a few kilograms cost from $3 000 to $10 000 and custom

built precision instruments from $20 000 to $125 000. Weighing systems which are a part

of a total system usually require a large

capital investment.

Table 4 is an estimate of the number of

devices which are used by state weights and measures officials, an activity which represents only one hierarchy system - that

associated with equity in trade. The systems

established within the Department of Defense

and by Department of Defense procurement

procedure are orders of magnitude larger.

Large mass standards, totaling in excess of

3 million pounds, are installed in various

deadweight machines used to calibrate

force measuring devices. There is no estimate of the total number of artifacts

which are used in the industrial or scientific community.

2.2.3 Reference Data

Reference data are defined to include all information or data which are taken from the

literature under the assumption that it is

applicable to the task at hand. Such data,

in general, are presented in a format which

is convenient to use. The format, however,

usually reflects judgments on the part of

the author which are rarely discussed in

detail. The ability to judge the validity of

the data relative to a particular usage is,

in many cases, beyond the capabilities of

the user either because of insufficient background on the part of the user, or lack of

detail discussion relative to the limitations

of the data, or lack of time. In many

instances the validity of the data is determined by the reputation of the author. Difficulties arise, however, when the judgments

of the author are not appropriate to the task

at hand.

Perhaps the largest body of reference

data are related to the "how to" of mass, volume and density measurements. Concepts

of measurement are introduced in the elementary grades and amplified in the high

school and early college sciences. The concepts are applied to practical measurement

tasks in text books and test procedures

throughout science and industry. For example, authoritative treatises on analytical

chemistry contains chapters or sections devoted to measurement detail [37, 38], weights

and measures officials receive formal instruction, defense department personnel are formally trained in calibration procedures.

Many industries conduct formal training in

the measurement techniques appropriate to their products. The result is a great confidence throughout the populace in the ability

to make mass, volume and density measurements. In reality, however, this confidence

is limited by the level of understanding of

the person who undertakes the task of

instructing the "how to" of measurement.

Tabular data on the density of both dry

and moist air are available in various metrological literature, such as the Smithsonian

Tables [39]. For requirements beyond the
accuracy of these tables, air density is

usually computed using supplemental measurements of pressure, temperature, and relative

humidity, and appropriate formulas. There are

sources of reference data which are adequate

for mass measurement. When such data are not

adequate for the materials under study, appropriate data are determined by separate

Table 2

Code Description 1972

V alue of Shipments (million of dollars ) 1971 1970 1969 1967 1963 1958

3811— Engineering and scientific

i nstruments

3811371 Laboratory precision

bal ances

3829321 Hydrometers, glass, all types

3229423 Scientific and Lab Glassware

3229425 Industrial and Technical

Glassware

3576-- Scales and balances,

except laboratory

3576011 Railroad track and motor

truck scales

3576021 Bench and portable industrial

scales

3576023 Floor scales (including

built-in)

3576025 Predetermined weighing and

check weighing scales

3576027 Automatic bulk weighing

3576029 Miscellaneous industrial

scales

3576031 Computing scales

3576035 Miscellaneous computing

scales

3576041 Bathroom scales

3576043 Person weighing scales

3576048 Miscellaneous kitchen, baby

scales

3576051 Mailing and parcel post

scales

3576082 Accessories and attachments

3576084 Parts for scales and balances

3576000 Miscellaneous household

scales and balances

8.1

92.5

62.4

1110.5 1215.9 1115.3 1049.0 722.1 758.6 ]

6.8 6.5 6.5 3.7

4.6

64.1

47.3

138.3 152.7 169.4 131.4 90.02 70.99

16.9 18.8 12.2 6.5

10.8 8.9 6.3 7.0

6.3 6.9 3.8 3.0

11.9 9.9 8.7

10.2

14.7

10.6

18.7

6.0

10.2 7.2

19.9

3.3

12.1

2.5

11.6

1.3

17.5

2.1 2.3

13.8

1.8

11.0

1.1 1.2

10.9

1.3

1.4

3.9 3.2 2.9 2.0

3.2

9.1

6.1

2.3

8.6

2.6

6.0

3.44 2.2

a number of published formulas, all of which

are adequate for some level of measurement.

There is evidence that a fundamental lack of

knowledge concerning the density of moist air

is one limiting factor on the transfer of mass value from an object made of a dense material to an object made of a light material,

e.g., platinum-i ridium alloy to stainless

steel, or single crystal silicon. [40]

Coefficients of expansion of metals are of

primary importance in length measurement and

in many scientific and industrial applications As a consequence, there are many

experiments which in turn become a part of

the reference data baseWater, and particularly distilled water,

is a reference material which is used for

many purposes in addition to volume and

density measurements. Tabular data regarding the density of water at various temperatures are available from many sources,

practically all of which are based on mea- surements made in the early 1900's. Changes

in the definition of the unit for volume and

in the temperature scale are not contained

in the older references. As mentioned

21
Table 3 Total Number of Number of Devices Retail Prices for New

Type of Device Devices in Use Produced in 1969 Devices (Average)

Drum computing scales 298,600 13,393 $275-525

Fan computing scales 74,800 3,073 $1 50-425

Projection scales 50,000 $800

Prepackaging computer scales 29,000 3,985 $3,200-5,600

Package checking 48,500 7,511 $225-243

Railroad track scales: 574 36 $16,000-30,000

Load Cell

Railroad track scales: 7,000 31 $17,000-40,000

Mechanical

Motor truck scales: 121 29 $3,000-7,000

Load Cell

Motor truck scales: 54,500 1 ,939 $3,000-10,000

Mechanical

Other Platform Scales: 282,894 22,810 $225-20,000

Load Cell and Mechanical

Beam Scales which have 4,720

capacities 100-1250 lbs.

Drum type computing and 3,320

automatic meter scales

Fan type computing scales 36,000

10 ton capacity vehicle 50

16 oz. beam scales 205,000

500 lb. parcel post scales 220

Table 4 Total Number Total Number

Type of Equipment in Use Type of Equipment in Use

Weight sets Test measures and provers

Cube weight sets (1/16 oz tc 2 lb) 841 1 gallon 1,312

Decimal pound weight kits 455 5 gallon 2,793

(0.001 lb to 0.3 lb) 50 gallon 251

Decimal ounce weight kits 127 100 gallon 380

(0.01 oz to 0.5 oz) 100 gallon (stainless 5 8 lb test weight kits 163 steel

)

Small individual mass standards 500 gallon 58

50 lb mass standard 36,647 1000 gallon 24

25 lb mass standard 191 Mi seel laneous test 300

Miscellaneous mass standard 140 measures and provers

Scales, balances, etc. Over and under 5 1

b

Package checking 726

10 lb field balance 305

Miscellaneous scales and balances 272

Platform scales 97

Large mass standards

500 lb mass standard 1,143

1000 lb mass standard 2,628

2500 lb mass standard 122

5000 lb mass standard 37

Miscellaneous mass standard 7 2500 lb dollies calibrated 36

5000 lb dollies calibrated 4 Miscellaneous moving dollies cali- 16

brated

22
before, NBS uses and recommends the tables

of Wagenbreth and Blanke [27].

Limitations on the density of water as a reference material are associated with the

isotopic content. Menache [41] and Emmet and

Miller [42] find that particular continental

waters vary in density as much as 10 ppm

because of isotopic composition. Information

on the variation at one place with time indicates a change of less than 1 ppm. The distillation process, however, may alter the

isotopic content of the waters. These limitations were in essence the reason for developing a solid object density reference

material (single crystal silicon) to be

described in section 2.2.4.

2.2.4 Reference Materials

Reference materials, that is, objects or materials which have been characterized by

careful measurement, are made available to

others for use in local measurement processes. In one sense calibrated mass and volume

artifacts, considered to be one of the instruments for mass measurement, could be

classified as reference materials. The re- mainder of the reference materials is associated with density measurements, primarily

the density of certain fluids.

Cook of the National Physical Laboratory

(NPL) studied the density of mercury. This

work included mercuries from various sources

as well as a mixture. In one study density

was determined by the hydrostatic weighing

method using a tungsten carbide cube, with

displacement volume computed from measured

dimensions. In the second study density was determined on the basis of the mass of mercury contained in a cubic volume constructed of

optically flat quartz plates, the computed

volume being based on interferometric length

measurements. The announced volume from the

density of mercury, uncertain by about

1 ppm, applies to the mixture. Sufficient

quantities of the mixture were furnished to various national laboratories for use in

precise pressure measurement.

Early work of Bowman, Schoonover and

Carroll using an instrument based on the

principles of the Cartesian Diver, demonstrated the ability to compare the densities

of small single crystal silicon artifacts to

a precision of 0.1 ppm. [43]. This work

suggested the possibility of using single

crystal silicon as a density reference.

Bowman et al . [8] determined the density of

selected large single crystal artifacts by

first computing the volume of a pair of

steel spheres from interferometric measurements of diameter. The volumetric ratio

method, which is essentially a hydrostatic

weighing but independent of the mass unit

and the density of the fluid, was used to es- tablish the displacement volumes of the

crystals. The uncertainty of the announced

density for these artifacts is on the order

of 1 ppm, the major components of which seem

to be associated with phase shift at the surface of the steel sphere in the interferometric measurements of their diameters and

perhaps the air density algorithm used to establish the mass of the silicon. All of

the characterized samples are on long term

loan or have been requested for loan by various national laboratories. Since the material is brittle it must be handled carefully.

Care must also be exercised in the preparation of the material for hydrostatic weighing. There are plans to characterize a larger quantity of this material and make it

available through the Standard Reference

Material program of NBS.

Oceanographers interested in relative

changes have established a reference material

designated Standard Mean Ocean Water (SMOW).

SMOW is taken from depths of 500 to 2,000

meters in open ocean areas where no direct

dilution by continental runoff or glacial

melt water can occur. Large bodies of data are based on SMOW from a particular location, however, samples from other areas taken at various times are adjusted to agree

with the established characteristics of

SMOW. Density is only one of the characteristics of interest. Samples of SMOW are available to oceanographers and available

from several sources.

2.2.5 Science and People

Mass, volume and density measurements, to- gether with length measurements, are some- what unique in the history of civilization.

Practical instruments for the measurement of

these quantities were essential to emergence

of the arts and crafts from the earliest

agrarian societies. Practical instruments

were essential to transition from barter to commerce in the form that we know it today,

first intertribal, then between communities,

and later between nations. Finally, practical instruments for the measurement of

these quantities were for centuries the most

precise instruments available which could be

used by philosophers and scientists for testing theories relating to natural phenomena.

The only common factor between these diverse

areas is the instrument, a situation which

resulted in growth of one of the most secretive crafts in the history of technology - that devoted to the development and manufacture of precision balances.

The characteristics of the three groups

of users, broadly designated as (1) the producers of goods and services, (2) the
regulators, and (3) the scientists, are such

that there is little intragroup communication

of significance. Producers of goods and ser- vices are profit oriented, that is, primarily

concerned with establishing and maintaining

a market for a product or a service. Their

success depends upon ingenuity in the application of science and technology in resolving

practical problems relating to the particular

product or product line. Competition, supported by antitrust regulation, makes it nec- essary to protect this ingenuity.

Professional engineering society meeting

agendas rarely include plant visits and even

then competitors must register separately.

Plant access is always restricted, except in

certain very large basic-type industries,

e.g., steel plants, automotive assembly

plants, large power plants, etc., with frequent interdepartmental restrictions. Except

for companies which conduct non-product re- lated research, communication within the area

of producing goods and services and with the

other two areas designated above, is generally limited to elements which are common to the group, such as problems relating to the

definition of "due care," e.g., test procedures, specifications, and "out of the

ordinary" contractual requirements. For the

average professional the peer group structure, if such exists, is related to these common elements.

In contrast, the scientific community is

entirely different. Generally, it is not

profit oriented. It is more or less dedicated to the advancement of knowledge rather

than the application of knowledge to the

solution of practical problems. The established review procedures associated with most

scientific literatures emphasize the peer

groups. The individual scientist in turn

relies on the quality of the literature of

his field and concentrates on contribution

to that literature base. In the design and

construction of apparatus he concentrates on minimizing the influence of measurement

variables which mask the property of interest. By exercising care in the definition

of the problem he is usually able to achieve

his goal supported in part by open discussion with interested colleagues, laboratory

visits, and participation in one or more established peer group activities.

The member of the regulatory group is not

interested in either the advancement of

knowledge or the application of that knowledge. He is concerned with the actions

which define a measurement relative to es- tablished laws and, in certain areas, to as- certain that measurements are made accordingly. He has essentially no interaction

with the scientific area. He does influence

the producers of goods and services in two

ways. In commercial transactions involving

the exchange of certain materials, contracts

can be challenged, in which case one defense

is evidence that the measurements were legally correct. As a protection against fraudulent and liability charges relating to the

goods and services produced, the producers of

such must conform to the legal interpretation

of what constitutes "due care." In these

matters if one has a choice between a defense

based on the justification of new procedures,

or on the precedence of old established procedures, the path of wisdom is usually the

latter.

These three groups have coexisted for the

last few centuries, relying on the guilds to

produce the necessary balances and weighing

devices. Events in the early 1800's resulted

in an attempt to impose an additional common

factor - the adoption of a uniform set of

measurement units. The units for mass and

volume were to be based on natural phenomena

rather than replicas of existing artifacts.

The scientists of the time could not agree on the basis for the length unit, e.g., the

length of a pendulum of a specified period or

a fraction of circumference of the earth as measured along a particular meridian. The

metric system, as developed in France, is

based on the latter, with the mass unit

based on the maximum density of pure water.

As a result of a fire England was faced with

the problem of replacing the accepted mass

unit. The resulting action, a reconstruction of the destroyed artifact, established

the pound as the mass unit for the English

speaking countries. This action favored the

producers of goods and services. Both the

construction of the metric units for mass and

length and the reconstruction of the pound were major scientific efforts.

With the completion of the artifacts the

dissemination mechanism in essence created

a new discipline - metrology. The metrologist was concerned with the conservation and

dissemination of the unit. The metrologist

utilized material from many sources in the

accomplishment of his assigned tasks. Scientists on occasion had found it necessary to improve mass measurements in order to ac- complish particular tasks. Using such literature, together with some engineering and

a lot of good judgment, the metrologist was able to make substantive contributions to the

literature with regard to improving balance

performance. He was, however, never really a part of any particular discipline. His

closest relationship was with the scientific

field. Scientists quickly adopted the metric

units whereas the technologists were and

still are reluctant to change. The metrologist also realized that solution to many of

his problems must come from the scientific

24
field, but he was frustrated by an inability to define his "real world" problems in

a manner which would attract the necessary

talent. His problems could not compete with

the exploding new field of modern physics.

He was not a part of the regulatory system,

but, by his position, he was the highest au- thority for decision. He was not a producer

of goods and services so that his judgments

relative to dissemination were not always

consistent with users intentions. He was

almost never challenged, either because of

his authoritative position or because usage

requirements had not caught up with measurement capabilities.

As with all other facets of the concept of mass, volume, and density measurements, the

science and people aspects have also experienced substantial change over the last few

decades. There are many factors which have

contributed to the change. Engineering curricula were changed drastically in the late

1940's and early 1950's. New disciplines

were established to bridge the gap between

science and engineering, e.g., engineering

science and engineering physics. The con- stancy of artifact mass units, a problem

which plagued the metrologist, essentially

disappeared with the adoption of stainless

steel. Computer technology took over much of

the routine drudgery of lengthy hand computations associated with precise measurement,

and for the first time it was possible for

the people involved in measurement to actually think about what they were doing.

Statistical techniques were developed to characterize a total measurement process

in the environment in which it had to be

used. At the same time emerging measurement

requirements, first associated with the space

age and later with environmental protection, were beyond the capabilities of currently

used measurement methods and established

mechanisms for inspection. As a consequence

the perceived role of the NBS mass and volume

section changed.

It was recognized that the data base and

methods of analysis used in characterizing

the processes used for maintaining and disseminating the mass unit could also be used

in other ways, and further, the principles

used had wide applicability in many measure- ment areas. It became possible to formulate

both the problems associated with precise

mass measurement and the suggestions for

those with practical mass measurement problems in such a manner as to attract the interest of the scientific community and

industry as well. The emerging synergistic

relationship is faced with many difficulties,

mostly associated with past practices,

however, it seems to be growing steadily.

25

2.3 Realized Measurement Capabilities

Any measurement result is the product

of a particular measurement process.

The quality of the results is generally

expressed by a quantitative statement

regarding the area of doubt, or uncertainty, associated with the result. The

magnitude of the uncertainty depends on two factors; the quality of the reference

standards, and the details of the particular measurement process. A necessary

condition imposed on the measurement

process is that the magnitude of the

uncertainty be acceptable relative to the manner in which the result is to be

used. Satisfying only this condition is not always sufficient. Other imposed con- ditions are related to compliance with

contractual requirements and conformance

with accepted practices, both of which

may or may not be of importance relative

to the intended usage. In most cases realized measurement capabilities are

not limited by either the available

standards or equipment but rather by

insufficient knowledge concerning the

performance of the process and concerning adequate acceptable limits relative

to the end use of the result.

2.3.1 Quality of Reference Standards

The reference standards for the mass

unit are the artifacts, or mechanisms,

which give the local measurement processes

access to the unit and multiples or fractions thereof. In size, reference standards range from fractions of a milligram

(small pieces of quartz fiber which must

be handled with a manipulator and a microscope) to large 50,000 lb stainless

steel discs, as used in the NBS force

generators. The quality of this array

must be judged from two viewpoints,

constancy relative to the precision of

measurement at a particular level, and

constancy relative to the intended usage.

In most cases, the latter viewpoint is

the most important.

The precision of measurement at the

prototype kilogram level (on the order

of .001 mg) is now such that changes in mass can be observed which reflect the

response of the material to the immediate

environment. [44] Cyclic changes seem to correlate with changes in pressure and

relative humidity. Constant rate increases

are attributed to contaminants in the atmosphere. Both of these are surface effects,

perhaps related to the catalytic properties

of platinum. These changes are significant

relative to the highest precision of
measurement (10 to 20 standard deviations).

Kilograms made from stainless steel do not

appear to vary as much as the platinum

iridium kilograms. Such changes are negligible relative to the precision of

most kilogram capacity balances (on the

order of .05 mg).

Before the general availability of

stainless steel, most weights used in precise weighings were made of brass. Constancy of mass was then a continuing

problem. First with the quality of the

brass, then with atmospheric corrosion,

and finally with coating materials and the

material used for adjustment. Lacquer

coatings were hygroscopic. Plating discontinuities and plating solution residue

caused variability. Oxidation of adjusting

material caused problems. NIBS Circular 547

delineated the detail requirements for

weights which would be accepted for calibration. Strict inspection and rejection

at NBS resulted in improved stability.

With the increasing use of stainless steel,

and the recent changes in instrument

design, constancy relative to most usage

requirements is no longer a problem.

Reference mass standards are available

in a variety of forms. Both regulatory and

competitive pressures have resulted in a hierarchial structure in which the quality

of a mass standard is judged on the basis

of its form and the difference between the mass of the weight and its assigned nominal

value--the adjustment tolerance. The highest order weights have the smallest adjustment tolerances, and in general, are more carefully constructed. The various levels

are frequently designated as primary,

secondary, tertiary, quarternary and so on down to the level of weights which are considered adequate for testing commercial

weighing devices. The hierarchial structure

exists primarily to satisfy the legal

requirements for the calibration of

weights, i.e. the comparison of weight

with a similar weight from a higher

echelon.

There are in excess of a dozen different

classes of weights, ordered by construction

detail and adjustment tolerance, the most

common being Class C- -Commercial Test

Weights. Table 5 shows the adjustment

tolerance limits originally established

in 1918. This tolerance structure has been

extended to include weights up to 10,000

lbs. It is of interest to note the influence of the crafts in the listing of

the customary units, many of which are

still in use but now defined relative to

the kilogram. (1 lb Avoirdupois, the

equivalent of 16 oz or 7,000 grains, is

defined as 0.45359237 kg; 1 apothecaries'

oz is 480 grains; 1 apothecaries' dram

is 60 grains; 1 apothecaries' scruple is

20 grains; 1 oz troy is 480 grains;

1 pennyweight is 24 grains; and one carot

is 200 mg.) To complete the picture, the

class C weights are typical of those used

to test commercial weighing devices to verify compliance with performance specifications shown in Table 6. A different hierarchy of adjustment

tolerances is used for laboratory mass

measurements. The commercial tolerance

structure tacitly assumes that the ambiguities associated with the concept and

the precision of the instruments are negligible relative to the size of the

tolerance. The tolerance structure

associated with precision weights is

frequently so small that both of the

above factors must be considered in detail

to verify compliance. This leads to a considerable degree of confusion in the

interpretation of calibration results.

One school of thought advocates strict

control of weight materials and designs in

order to maintain the simplicity of hierarchial structure relative to weight sets,

generally at the expense of the user. The

competing school of thought, believing that

one should be able to assign a mass value

to any object reasonably stable in mass

properties, advocates the abolishment of

the hierarchy beyond the requirements of

commercial weighing.

In summary, mass standards are available

which are sufficiently stable in mass for

all known requirements. This fact is

generally down graded in the manner in

which the mass value is assigned to the

standards. The variety of adjustment

tolerance structures is confusing to those

who must obtain standards with reference

to a particular usage. An ASTM subcommittee

has been working on the task of unifying

and simplifying the various specifications.

While this document is now nearing

completion, the growing acceptance of the

direct reading instruments has greatly

reduced the priority initially attached

to the task. The problem, however,

remains in areas which utilize a hierarchy

of mass standards. For an increasing

number of users, the reference mass standards are the "built-in" weights in

the modern balances. These weights are

of good quality and are carefully adjusted

to well within the established tolerances.

Generally it is not possible to calibrate

such instruments in the traditional manner,

i.e. the use of hierarchy standards.

Reference standards for glass volumetric

apparatus consists of volumetric and measurement pipets, volumetric flasks and

26
TABLE 5 —Toleraaces for Class C—Commercial Test Weights

[The maximum error allowable on each weight is tiven in the co!:^n^s hcacl'-d " Tolerance"]

Customary

Avoirdupois

1

I

' Grams 1 Apothecary I Ounces troy ; PeunyveigilU

I I !

Carats

Tecoinitslic-Q

Tcler- auce

Denomination Ttoler- ance

Denomination Ttoler- 1 ance

Denomination

Toler- ance

Der.omi- nariGn

Toler- ance

Denomination

toler- ance

Denomlaiition Ttoler- ance

-

lb. gr. gr. gr. oi. ap. gr. 02. t. gr. dv.-t. gr. c mg

600 50 10 10 000 1 12 1 1000 10 10 000 10 2500 70

10 409 25 6 soeo 1 10 1 500 10 5000 5 2000 60

5 250 20 6 2000 0. 5 6 0. 5 400 5 4000 5 1000 40

2 150 10 4 1000 0. 3 5 0. 5 300 5 30C0 3 500 30

100 a 3 500 0. 2 4 0. 5 200 5 2000 3 200 20

5 3 200 0. 15 3 0. 4 100 3 1000 2 100 10

500 70 4 2 100 0. 10 2 0. 3 50 2 500 1. 5 50 7 200 40 3 2 50 0. 05 1 0. 2 40 1. 5 400 1 0 20 5 100 30 2 1 5 20 0. 03 r. ap 30 1. 5 300 1 0 10 3

50 20 1 1.0 10 0. 02 0.2 20 1.0 200 1.0 5 2

20 _ 10 oz 5 0. 015 5 0. 2 10 1.0 100 0. 5 2 10 7 10 1.0 2 0. 010 4 0. 2 5 as 50 0 t 1 0 7

5 3 8 0.5 1 0. 005 3 0. 1 4 0. 5 40 0.3 0.5 0. 5

2 3 S 0.5 0 5 0. 005 2 0.1 3 0.4 30 0.3 0. 2 0. 3

1 2 4 C. 5 0 2 0. 0C25 1 0.05 2 0.3 20 0 2 O 1 0. 2

2 0. 3 0. 1 0. 0020 =. ap. 1 0. 2 10 0. 2 0. OS 0.15

500 1. 5 I 0.2 0. 05 0. 0)15 2 0.05 0.5 0.2 5 0. 1 0. 02 0. 10 200 0.7 t 0.2 0.02 0. 0015 1 0. 03 0.4 0. 15 4 0. 1 0.01 O.OS

100 0.5 a l 0.01 0. 0015 0.3 0. 10 3 0 05

50 0. 35 i

0. 05 0 2 0. 10 2 0. 05

2il 0. 20 0.05 0 I 0.05 1 0.03

10 0. 15 a (is 0.05 0. (53 5 0. 10 0.02 0. 0» 0. 025

2 0. 05 0.03 0.025

1 0. 04 0.02 0. 020

0. 01 0. 015

0. 005 0. 010

0. 004 0 COS 0.003 0. C07 0.002 0. 005 0.001 0. OOS

straight precision burets. Perhaps the

major factors differentiating the quality

of such glassware are related to the index

mark which defines the contained volume

the quality of the mark, its location,

and permanence. The user must set the level

of the miniscus to coincide with the plane

established by the index by adding or removing small quantities of liquid. He

is interested in the quantity of liquid

in the vessel when this condition has been

satisfied. In the case of precision glassware, the location of the index is established by actual test. In the case of

burets, there may be several test points

which are subdivided linearly in the

marking process. The reference standards

are the basis of a variety of glassware

which is graded according to the quality

of the marking, and the difference between

the actual volume contained relative to a particular index and the nominal volume.

The useful life of all glassware, including the reference standards depends on breakage and the cost of cleaning.

The present manufacturing processes

produce glassware which is in accordance

with current specifications. These specifications generally contain both perfor- mance and detail requirements. The sales

groups favor the detail requirements but

when basic manufacturing methods are changed, the ware produced may no longer

comply with specifications. This situation

is usually resolved by a concentrated

effort to change the specification. For

example, changing from an etched and filled

index to a "fired on" index requires a change in Handbook 44 if the ware is to be

acceptable to the state weights and measures officials.

Precision volumetric glassware is basic

to the current methods for the preparation

of solutions in "wet" chemistry and clinical pathology. Testing of this apparatus

for compliance with specifications or for

adequacy relative to a particular requirement is now within the capability of most

users with one exception. A legal measure- ment as defined by the regulators requires

an artifact which has been calibrated by

higher authority. The calibration efforts

of NBS exist essentially to support the

states weights and measures operations

with only occasional requests for calibrations relative to a particular end use. For example, some calibration work directly

supports manufacturers quality control

systems.

Metal capacity standards, e.g. "slicker

plate" containers, cubic foot bottles and

provers, are used either singly or in

combination to test flow metering devices,

or in the calibration of large tanks. The

devices are compromises between the properties one would like to have in a standard,

27
TABLE 6—TYPICAL BASIC TOLERANCES FOR SCALES INDICATING OR RECORDING IN AVOIRDUPOIS UNITS

(Edited, for complete table see NBS Handbook 44, pages 19, 20, 21)

Test load Mai ntenance tol erances Acceptance tolerances

From To*

Ounces avdp. Grains Ounces Pounds Grains Ounces Pounds

0 2 2 1 2 4 4 2 4 8 8 4 8 16 16 8

Pounds avdp.

1 2 25 1/16 0.004 13 1/32 0.002

2 4 1/8 .008 1/16 .004

4 7 3/16 .012 3/32 .006

7 10 1/4 .016 1/8 .008

50 75 1 .062 1/2 .031 75 100 1 1/2 .094 3/4 .047

100 150 2 .125 1 .062

800 1 ,000 14 .875 7 .438

1 ,000 and over 0.1 percent of test load 0.05 percent of test load

* but not including

BASIC TOLERANCES FOR SPECIAL SCALES INDICATING OR RECORDING IN AVOIRDUPOIS UNITS

Type scale Maintenance tolerances Acceptance tolerances

0.1 percent of test load

0.05 percent of test load

0.3 grain

0.2 percent of test load 0.1 percent of test load

Prescri ption

Jewelers

Cream and moisture

Test (18 gm load)

Animal, livestock,

crane, axle-load,

hopper (other than

grain) and vehicle

Railway track scales

static

uncoupled in-motion

Wheel load weighers

Railway coupled inmotion (100 car

test train)

0.1 percent of test load

0.05 percent of test load

0.5 grain

0.2 percent of test load

0.2 percent of test load

3.0 percent of test load

0.1 percent of test load

0.2 percent of test load

2.0 percent of test load

Acceptance and Maintenance Tolerances

a) Difference between motion weight and static weight

of train shall not exceed 0.2 percent.

b) Difference between motion weight and static weight

on 100 car weights shall not exceed.

1) 0.2 percent on 30 cars

2) 0.5 percent on 5 cars

3) 1.0 percent on any car

28
and the ability to handle the standard in use- "Slicker plate" standards use a flat

glass plate on a flat surface of the con- tainer to define the contained volume.

Such artifacts are usually of heavy con- struction and are limited in size to at most a few gallons. Capacity standards

are of lighter construction, the location

of the liquid level in the neck being

inferred from the liquid level in a parallel glass tube with reference to an appropriate linear scale mounted on the vessel.

The calibration may consist of determining

the volume relative to the scale reading,

or the adjustment of the scale to a position appropriate to a nominal volume and

then determine the "over" and "under"

amounts relative to appropriate scale

graduations. There is no formal hierarchy

of capacity standards. The manufacturers,

of which there are only a few, can furnish

calibrated standards adequate for most

requirements. In some specific uses, such

as in the petroleum industry, the items are routinely sent to NBS for calibration.

Reference standards for density

measurements include picnometers, reference

fluids, solid objects of measured density,

and calibrated hydrometers. Hydrometer

sensitivity to change in density is

determined by the ratio of the cross

sectional area of the stem to the displacement volume of the bulb, and,

consequently, the instruments are fragile.

A high quality hydrometer has a hand

marked scale permanently enclosed and

anchored in the stem. The calibration is

for a given liquid at a specified temperature. Corrections are necessary for

other liquids (surface tension correction)

and other temperatures.

2.3.2 The Measurement Process

and procedures. This is not to suggest

that all measurements should be made ac- cording to these published techniques but

rather to identify the magnitude of variability from various sources which the user must evaluate relative to the manner in

which he intends to use his result. Ultimately, the uncertainty associated with

his result is based on three factors, the

systematic error introduced into his

process by NBS calibrated standards, and

the systematic error and random error associated with his process. If one or both of the latter factors are the predominant terms in his uncertainty, technically

there is little need for direct contact

with NBS. For example, the Class C toler- ance for 1 kg from Table 5 is 100 mg.

TABLE 7—TYPICAL MEASUREMENT

UNCERTAINTIES

Mass

Level

50 000 lb

50 lb

1

1

1

kg

gmg

Uncertainty

+ .2 lb + .000 03 lb

+ .11 mg

+ .003 mg

+ .000 5 mg

Large Capacity Measures

Test Tank 3 000 liters*

100 gal prover

30 gal prover

5 gal "Slicker Plate"

+ 1 liter

+ .000 20 gal + .000 33 gal + .000 31 gal

Displacement Volume

Alumi num Kg

Volumetric Glassware

1 Liter Flask

360 + .000 5 cm

+ .1 cm

A measurement process includes the

instrument, and all of the measurement

details including preparation of material,

making the observations, supplementing

data, data analysis, and interpretation.

The NBS measurement processes for mass, volume and density are sufficiently well

characterized that the uncertainty statements are based on quantitative values

for random and systematic error which are based on large collections of data

reflecting both current and past performance. Typical measurement uncertainties

are shown in Table 7. It has been the intent to completely

describe the various measurement processes

in the literature to demonstrate the mea- surement capabilities which can be achieved

with currently available instrumentation

50 ml Buret + .01 cm

10 ml Buret + .005 cm

25 ml to

50 ml Transfer Pipet + .01 cm

Hydrometers

API Scale Range 10 to

21 in .1 API + .92 API

Specific Gravity

Scale Division .0005 + .0001

Alcoholometer 56-72

%vol. in A% Divisions + .02%

3 *The recommended SI unit for volume is m . In practice, however, the term "liter"

is used for one cubic decimeter, and

milliliter (ml) for one cm^.

29
The uncertainty associated with a calibration

of the same weight from Table 7 is .11 mg.

If compliance with Class C is adequate for

his intended usage, the esthetics of an NBS calibration is a costly luxury. Nonetheless, for reasons associated with com- pliance or conformance, it may be necessary

for the user to have standards calibrated

periodically at NBS.

2.4 Dissemination and Enforcement Network

There are a number of networks more or less loosely interlocked. By virtue of

the embodiment of the mass unit in artifact standards, NBS is the focal point of

the network concerned with the dissemination of the unit. The dissemination of

methods, or the "how to" of measurement

has in the past been the literature of

the various disciplines, i.e. chemistry,

clinical pathology, etc. The most widely

recognized enforcement network is that

associated with equity in trade, a responsibility delegated to the individual

states. Other enforcement networks have

been established by various segments of the

government such as the Department of

Defense, the Internal Revenue Service,

the Nuclear Regulatory Commission and

others. A different type of enforcement

network is that associated with voluntary

or consensus standards, mostly concerned

with the "how to" of measurement. With

the emergence of the concept of measurement as a production process, a concept

which concentrates on the adequacy of field

measurements relative to the intended

usage, the role of the Mass and Volume

Section relative to these various networks

is quite complex.

2.4.1 Central Standards Authorities

The units, as defined by the Convention

of the Metre and the Committee General

e

dis Poids and Mesures, were declared

legally permissible in the U.S. by Congressional action in 1866. This action was

followed in 1893 by the Mendenhall Order

in which the Secretary of the Treasury

announced that the International prototype standards for mass and length would

be regarded as fundamental standards. The

practical mass unit in the U.S. is embodied

in a pair of ni chrome kilograms. In the

dissemination of the unit, the Mass and

Volume section is not concerned with the

conformance of the reference mass standards

to any specification requirement for

construction or adjustment tolerance. The

perceived role of the Mass and Volume

section is to establish mass values for

any object sufficiently stable in mass to warrant the calibration effort. The calibrated objects, in turn, provide fixed

reference points on a hypothetical mass

scale such that others can adjust working

weights to whatever tolerance desired.

A second class of de facto central

standard authorities have been established

by various levels of the Federal Government. Of these, the two of largest impact

are the Federal Procurement Specification,

as issued by the General Services Administration, and the regulations of the Department of Defense, previously mentioned. In the former case, GSA acts as a mediator

between the federal user and the supplier

to obtain products which are adequate for

the intended use. Federal specifications,

unlike voluntary standards, address the

quality control aspects of procurement and

clearly delineate the basis on which a product will be accepted or rejected. The

DoD regulations with regard to measurements

also stem from the generic problem of

quality control with respect to military

procurement.

2.4.2 State and Local Offices of Weights

and Measures

One of the largest central authorities

is the National Conference of Weights and

Measures, an organization of state and

local weights and measures officials. The

historical tie between NBS and NCWM is

long standing. The Constitution of the

United States, Article I, Section 8,

empowers Congress ". . . . to fix the

standards of weights and measures."

Congress has chosen to allow the individual

states to perform this function. However,

as early as 1836, Congress, in a joint

resolution, directed the Treasury to fabricate standards for customhouses and

states and to establish an Office of

Weights. In 1901, this office was designated as the National Bureau of

Standards. As the nation grew, a need was

felt for a closer coordination of the

state activities and the National Bureau

of Standards met with state officials to

discuss "protecting the public against

short weight or measure." A dialogue

developed which is now carried out through

the agency of the National Conference of

Weights and Measures.

A typical state Office of Weights and

Measures is a unit in the state Department of Agriculture although it may be

under the Department of Law and Public

Safety (New Jersey), Department of Labor

(Rhode Island), Department of Commerce

(Arkansas), or elsewhere. It is headed
by an appointed state official and has a staff of inspectors which varies according

to the size of the state by at most a few

dozen.

Within the state, various local

jurisdictions may also have weights and measures authority. In all, there are a total of 775 offices and a total of approximately 3000 officials. Besides controlling the weights and measures activities of

retail trade, depending on the state's

industry, anhydrous ammonia (fertilizer) or lumber or grain may be of official

interest. Recently, under both the Fair

Packaging and Labeling Act of 1966 and

the general use of consumerism, these

offices are increasingly involved in con- sumer protection in areas remote from

classical weights and measures activities.

In 1965 Congress appropriated funds to equip state laboratories with standards

whose values were known with uncertainties

smaller than those needed to support the

tolerances mentioned in section 2.3. This

program, managed by the NBS Office of

Weights and Measures but calling on other

NBS resources, has to date delivered 42 of

the 53 sets of artifacts and instruments

needed by U.S. states, territories, and

the District of Columbia.

Provisions of this law call for the

states as a prerequisite for the award to supply a suitable laboratory and trained

metrologists. In the absence of educational facilities noted before, a training program has been established to provide initial and continuing education

for weights and measures officials and

technicians. Only the State of California

has a comprehensive in-state program and

less than 6 states have a full time training officer, although some twenty states

have a program of some sort. The state weights and measures offices

provide a calibration service for mass which is accessible to the general user community in addition to performing such

services for their own inspection operations. The NBS interfaces with this

system only through contact with certain

users who have tried these services with

inadequate results. The impression is

that the service is seldom used where the

uncertainty of the measurement must be

known. The service is a convenient way

to comply with certain imposed requirements, however, with few exceptions, the

facilities are not oriented to end use

probl ems.

2.4.3 Standards and Testing Laboratories

and Services

Weight and balance manufacturers offer

calibration services, i.e. tests for com- pliance with or adjustment to comply with,

tolerance specifications for both weight

sets and weights internal to certain

balances, with reports which are acceptable

for most requirements. The world's largest

supplier of precision balances (by far in excess of 50% of the market) relies on NBS

for the maintenance of their standards.

Maintenance and test of weighing equipment

is usually done by separate organizational

units in large facilities, or by service

contracts with reputable repair service

organizations, e.g., those made available

by the instrument manufacturer. Metal

volumetric apparatus manufacturers, of

which there are only a few, provide both

refurbishing services and calibration

services.

The production of precision glassware is

controlled at the manufacturing level by

the same methods as used in NBS calibration. The manufacturer guarantees compliance with federal specifications. These

specifications, in turn, can be used by

anyone in the procurement of apparatus.

GSA has established procedures to monitor

the quality of the products. Considering

the normal breakage rate and the increasing

use of "throw away" apparatus, there is

little motivation for testing services to calibrate apparatus.

Attempts to interest independent testing

laboratories in providing calibration ser- vices, particularly with regard to hydrometers, have not been successful. These

laboratories are primarily concerned with

performing specification tests according to procedures prescribed by ASTM, The American

Concrete Institute, The American Welding

Society, etc. Either the volume of work

is too small relative to the cost of establishing a service, or the nature of the

industry using the instruments is such that

the risk is too large with respect to the

profits. Of approximately 130 members of

the American Council of Independent

Laboratories, less than ten list weighing

as a particular specialty.

There are a few companies, some worldwide, who provide calibration services

to the petroleum industry. The services,

consisting of meter and tank calibrations,

contract directly with the oil companies.

It is presumed that these companies exist

31
because of the necessity of the oil com- panies to meet various regulatory requirements, in which case it is less expensive

to contract for the services than to establish their own service organizations. By

far, most of the large oil and pipeline

companies have their own service

organizations.

The primary function of the echelon

calibration laboratories of the Department

of Defense (DoD) is to provide calibration

and testing facilities to the various

branches of the department. With few

exceptions, e.g. government owned equipment and certain support to defense con- tractors, these services are not generally

available to the user community at large.

Cooperation with local weights and measures

officials, and with local industry is largely dependent upon the work load and

the attitude of the local command. Similar

services are provided to the National Aeronautics and Space Administration contractors through a series of contract operated

facilities. All of the top echelon laboratories in these two networks are participants in the Mass Measurement Assurance

Program.

2.4.4 Regulatory Agencies

Regulatory agencies are concerned with

the application of measurement technology

to certain specific measurements. Generally, the uncertainty associated with the

measurement result is only one factor in

judging the adequacy of the measurement.

Regulatory agencies view measurements in one of two ways. One view typical of the

older agencies is defensive in nature. In this view, in the event of prosecution, the use of NBS calibrated standards is considered to be a means to divert attention from

the measurement detail, i.e. the adequacy

of the measurement is established by "traceability" of the unit. Requirements established by the newer regulatory agencies

tend to emphasize the uncertainty of the

measurement result relative to the manner

in which the result is to be used, i.e. the

adequacy of the measurement is established

by "traceability" of the measurement. In this case the adequacy of the measurement

result is established by careful analysis

of the entire process including standards,

methods, control of systematic errors, etc.

In these cases NBS involvement is primarily

consultation. The standards may or may not be NBS calibrated.

State weights and measures regulations

are typical of the former viewpoint men- tioned above. Regulatory agencies which

are concerned with limiting concentrations

32

of harmful substances, such as the Environmental Protection Agency and the Nuclear

Regulatory Commission, are examples of the

latter viewpoint. The Nuclear Regulatory

agencies have worked closely with the Mass

and Volume Section since special nuclear

materials accounting procedures require and

use both mass and volume measurements using

state-of-the-art techniques.

The Mass and Volume Section has been

aggressive in encouraging the regulatory

agencies to change from a "traceability

of the unit" concept of measurement to a "traceability of the measurement" concept.

The following examples are illustrative of

the nature of the transition.

The recognition of adequacy relative to the manner in which the result is to be

used is illustrated by the work with the

Internal Revenue Service's Division of

Alcohol, Tobacco and Firearms Control. The

function is the control of the use of ethyl

alcohol. All legal ethyl alcohol is manu- factured under bond. No matter what the use of this alcohol, be it beverage,

medicinal, cosmetics, or any other purpose,

it is taxed at the time of withdrawal from

bond on the basis of equivalent 100 proof

gallons (i.e. a 100 proof mixture is a fifty percent mixture with water). The

determination of proof at the time of withdrawal is a consensus between the IRS, the

supplier and the purchaser. The measurements are made with "proof" hydrometers.

From the IRS viewpoint, the required precision of measurement is established by the

proof increments in the tax tables. Modification of these procedures are used in the case of wine and similar alcoholic beverages. There is a mechanism for tax rebate

where ethyl alcohol is not used as a beverage. Over the years under the guidance of

NBS, IRS has established a calibration

service adequate to support these activities. On occasion NBS acts as a consultant

in regard to techniques and basic data.

The producers and purchasers of the

material, however, rely on the NBS hydrometer calibration services.

Finally, the work on voluntary standards

relative to the nuclear industry (Institute

for Nuclear Materials Management and the

Nuclear Regulatory Commission) is an example of an area where perceived measurement requirements are beyond the capabilities of traditional weights and measures

regulatory procedures. In this case NBS

has been involved in helping both the regulated and the regulator to (1) quantify

the requirement and (2) understand the

concept of measurement as a production

process and measurement assurance and

(3) ways and means to improve measurement
techniques in both mass and volume

measurements.

2.5 Organizational Input-Output Matrix

In an attempt to more clearly define the

morphology of this measurement system, we

have created an Input-Output Measurements

Transactions Matrix. This matrix presents

in compact form all we have been able to

deduce about the interconnections in our system and it justifies careful study.

Along the upper and left hand border of

the matrix you will find twenty-five organizations or groups which have been identified

as potential users or suppliers of measurement data in the field of mass, volume, and

density. Many of these are both users and

suppliers. In their role as suppliers, they

appear on the left, as users along the top

border.

By survey, by interview, by a retrospective study of NBS calibration records, and

by the experience of the authors, the interactions between these elements of the system

were estimated and quantified according to the code at the bottom. The interactions

were examined for magnitude, derivative of

the magnitude, and importance to the system's well-being. Particular care was exer- cised to maintain a uniform scale of values,

particularly relative magnitudes. It is

realized that this scale reflects a degree

of subjective judgment even though utilizing the individual opinions of several knowledgeable people independently.

First, as a supplier of measurement information, we note, not surprisingly since

our charge is measurement, that NBS interacts strongly with most of the other elements. Only a few industries are blank.

These are industries where mass, volume, and

density measurements are not frequently

made. Our interactions with the knowledge

community, for example, is strong, stable,

important and moderately successful.

NBS as a rule seems to listen fairly well

to what people have to say. Except for the

knowledge community and the upper echelons

of the standards bodies, these transactions

are largely assessments of perceived needs.

3. IMPACT, STATUS AND TRENDS OF

MEASUREMENT SYSTEM

The national measurement system for

mass, volume and density, being defined as the totality of all such measurement

processes from the defining standards to the point of ultimate usage, is so vast

that further subdivision is necessary

before one can address impact, status and

trends. One can identify three subsystems

on the basis of the manner in which the

results are used, one relating to the

determination of quantity of material; one relating to matters concerning regulation

and quality control; and one relating to properties of objects or materials. While

these systems are not completely independent, the structures reflect practical

boundary conditions associated with the

desired result. Within this structure, the

impact, status and trends of the subsystem

can only be discussed relative to the

desired result. All mass, volume and

density measurements are merely one of many

elements involved in a variety of specific

endeavors. In at least two of the above

subsystems success is not limited by the

precision of measurement, but rather by

social and economic judgments.

3.1 Impact of Measurements

3.1.1 Applications

Every legal exchange of material, be it

at the local market or in the world trade

arena, has two elements, the price and the

quantity of material. The same is also

true in the exchange of products except

where the product is marketed as a unit.

As a consequence, there is at least one, and in some cases many, determinations of

quantity for each transaction, and the cost

of measurement is a part of the cost of

doing business. Order in the marketplace

is contingent on the acceptance of uniform

measurement procedures. The major con- straints on the resulting measurement

processes are the cost of measurement

relative to the cost of the material, the

constancy of the mass, or volume, of the

material over the interval between shipment and receipt, and the ability to make

adequate measurements in the environments

associated with custody exchange. In all cases the measurements must be within the

capabilities of the available personnel and

be defendable in court, that is, in accordance with a consensus agreement and relative to an acceptable artifact standard.

Direct NBS involvement with this subsystem

is providing access to artifact standards

which are accepted as authoritative. In- direct involvement by NBS is associated

with the availability of instrumentation

and measurement methods.

The subsystem concerned with quantity

measurements is very large and diverse. It includes those activities in which the end

product is formulated by recipe, including

the preparation of solutions in the chemistry laboratory to the bulk production of

paints, acids, beverages and other liquid

33
DIRECT MEASUREMENTS

TRANSACTIONS

MATRIX FOR

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1 KEY TO MATRIX ENTRIES

C - IMPORTANCE OF TRANSACTIONS

1 = Purely convenience

2 = Strongly desirable

3 = No real alternatives

4 = Essential

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N = Declining

0 = Stable

2 = Growing

4 = Growing explosively

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D - ( IN) ADEQUACY OF SERVICES

0 = No improvements needed

1 = Could be improved

2 = Marginal

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Tri vial

Minor

Moderate

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34
products- These measurements are subject

to essentially the same constraints as those associated with the exchange of

goods, except that the cost of measurement

is established relative to the quality and

market value of the end product. The NBS

role, however, is essentially the same. The subsystem associated with quality

control and regulation is also a diverse

subsystem with a different set of constraints. A characteristic of such mea- surements is that the measurement effort is

defensive rather than productive. The con- cern is generally whether the measurements

are adequate for the purpose, or whether

the product does or will conform to the

appropriate specification. Decisions con- cerning the details of the measurement

process are relative to risk. The generation of the elements of the subsystem arise

from social pressures, the need for product

acceptance, the need for national defense,

and the health and welfare of the nation.

Three subelements, discussed below, illustrate the NBS role with regard to this

subsystem.

Perhaps the oldest of the elements is

that associated with weights and measures--

the states weights and measures activities.

Constraints on the system are those associated with the legality of measurement, the

need for viability, the need for simplicity, i.e. parties involved must understand

the detail, and the resulting procedures

must be within the capabilities of the

available personnel. The net results in a labor intensive system which operates most

effectively at the consumer level, and with

great difficulty in interactions with

capital intensive organizations. NBS has

supported this system by providing well

calibrated reference standards for mass

and volume, and good instrumentation.

By and large, this equipment supports an echelon of field standards.

A second element associated with quality

control is the system established by the

Department of Defense. One of the unique

characteristics of this element is that the

established system at any given time must

be capable of immediate expansion, thus it

is very similar to the weights and measures

elements, with echelons of calibration laboratories. Each laboratory maintains

standards of mass and a measurement capability appropriate to the echelon, partly

to support the various commands, and partly

in anticipation of immediate expansion.

Visibility is in the form of calibration

intervals and inspection "marks." One can argue the cost effectiveness of such a system, however, in the event of rapid

expansion, a simple inspection system based

on manufacturer's specification which can

be maintained with minimum training is

better than nothing. A more complex

system, based on the premise that completely trained metrologists will be available,

would tend to collapse from the lack of

adequate manpower. There are other ramifications, previously discussed relating to

"due care." The element is large, and

through inertia, the features have been

adopted in other disciplines, i.e. American

College of Clinical Pathology.

The third element consists of the mea- surement processes associated with regulation other than weights and measures. Some

of these systems, those associated normally

with compliance, have features from both

the weights and measures, and the military

systems. All are concerned with legality

of measurement. The one component with

which the Mass and Volume Section has the

most direct input is associated with the

control of nuclear material. In this case, the source of detail specification is the

regulated facility. The regulator, usually

the Nuclear Regulatory Commission, generally provides only guidelines and goals. In the process of establishing a facility,

detailed procedures are submitted for re- view and approval. The collection of

approved procedures eventually becomes the

operation manual. The role of the inspector is that of enforcing compliance with

the approved procedures. This approach is

also being considered in regulations con- cerning the introduction of pollutants into

the atmosphere. In this element, the

people being regulated have considerably

more interest in measurement detail. The

decisions, however, are theirs relative to the economics of measurement, including

the maintenance of the system, and the

announced goals established by the regulator. Generally, the desired precision of

measurement is somewhat beyond that

associated with either weights measures

and military procurement with respect to mass and volume.

The last subsystem, those concerned

with the properties of objects or materials, is also a large diverse system. The

elements of this system are mostly con- cerned with adequacy of the result of

measurement relative to a particular

requirement, that is, the uncertainty

associated with the measurement result as compared to functional limits related to the task at hand. In essence these are

the processes associated with the product

which in turn are monitored by the various

quality control and regulatory systems, if

such exist. These measurement processes

range from those associated with the

35
constancy of the defining mass unit, to the

determination of the density of dislocation

free single crystal silicon, to the support

of force and pressure measurements. Some

of these processes are concerned with properties of special materials, such as the

density of crude oil and refined petroleum

products, the results being the basis of

measurement systems relating to both regulation and commerce. Measurement processes

in this element are usually free of all

constraints other than that of producing

adequate results in the most economical manner.

3.1.2 Economic Impacts

3.1.2.1 Processes Relating to Quantities of

Material

In a free economy one factor contributing

to the stability of the marketplace is the

ability to make adequate measurements of

quantity. The system that has evolved

places NBS in the role of higher authority

with regard to measurement standards while

generally reserving the right for decisions

with regard to measurement detail. Considering the intricacies of the judgment

factors this perhaps is as it should be.

There are adequate techniques for the measurements which have to be made. The dollar

volume associated with exchange of material

is a significant fraction of the gross

national product. Yet direct NBS interaction is minuscule. On the other hand, this

subsystem is not receptive to attempts to establish self-sufficiency. Change in the

cost of materials or changes in regulatory

requirements are the major motivating

factors for improvement. It is clear that

NBS visibility is desired, and on occasion

aggressively pursued, yet direct economic

benefits remain intangible.

3.1.2.2 Processes Associated With Quality

Control and Regulation

In both cases, the investment in

measurement processes is associated with

the entrepreneur's assessment of risk and

not by the available precision of measurement. This follows from the fact that

neither function exists until such time

that there are facilities capable of production of parts or products more or less

adequate for the introduced usage. Professional Quality Control people and

inspectors are not generally trained

metrologists. In both cases the assessment

of the effectiveness of the efforts are measured in terms of compliance with the

established plan rather than the effectiveness of the effort relative to what the

effort is expected to accomplish. In the

interface between the producer and the consumer, and between the regulator and the

regulated, the visibility of NBS seems to be highly desired, particularly in the form

of calibrated standards. On occasion, NBS

calibration is used to resolve disputes in

lieu of other legal action. As before, the

cost of the NBS services provided is minuscule relative to the value of the goods

subject to quality control and regulation.

Again, this subsystem is not receptive to efforts directed toward establishing selfsufficiency. Aggressive attempts to improve the utilization of both methods and

instrumentation have not only been resisted

but met with animosity. In contrast to the

previous subsystem, it is felt that this area would welcome NBS expansion of routine

calibrations, not from the standpoint of

product improvement, but from the resulting

simplification of paperwork requirements.

3.1.2.3 Processes Associated With

Properties of Objects or Materials

The processes in which mass, as an intrinsic property of a material or an object is of interest require the ultimate

in mass measurement capabilities, e.g.,

the constancy of the defining artifacts

and the density of single crystal silicon.

These processes are without exception within

the scientific community and in support of

specific scientific goals, e.g., the determination of Avagadro's Number, the realization of certain electrical quantities, the

gas constant, the universal gravitational

constant and the like. While a substantial part of the total effort in mass, volume and density measurements at NBS has

been in support of these efforts, the direct economic impact resulting from this

effort cannot be measured at this point

in time. This does not mean that these

efforts are totally devoid of such benefit.

The emergence of new procedures and refer- ence materials as a result of this work

reduces the cost of certain types of measurements, e.g., the "solid object" density

standard. In the course of this work, the

efforts devoted to understanding the philosophies of measurement, in addition to development of procedures, have the greatest

potential for economic impact on the entire

measurement community.

3.1.3 Social Impacts

The greatest impact of the Mass, Volume,

and Density system to the average citizen

lies in the area of retail trade. Thanks to

36
a functioning weights and measures enforcement system, the citizen in his daily life can rest assured that he can base his purchasing decisions on posted price-per-um't

quantity. It is not necessary to search for

the gas station giving the largest gallon

and prepackaged foods can be bought without

qualm. Yet, this state of affairs is not

without cost. In 1972-73, the State of

California reported litigation costs of over

$100,000 in a single "short weight" case.

In the same year, the State of New Jersey

reported 1,321 citizen complaints of which

1,183 were successfully prosecuted with

$54,750 in penalties assessed. The State of

West Virginia reports over $60,000 recovered

for consumers. Most of the populace have some knowledge of the general concepts of

these measurements, and a large percentage

are involved in some degree through such

things as keeping track of body weight,

procuring supplies and materials, and formulating various recipes. Marketing practices have changed substantially over the

past two decades, however, and with the

preponderance of prepared and prepacked

foods, pricing scales interfaced with

computers, etc., the populace must rely

largely on the system to look after his

interests. Systems, on the other hand, tend

to be inflexible, bureaucratic and not generally sensitive to individual problems.

Achieving and maintaining order in the

marketplaces through a bureaucratic structure is not without cost. The degree of

uniformity in available products and prices

across the country is one of the characteristics noted by many foreign visitors.

Sizable as these numbers are, they are

a vanishingly small fraction of total

sales. It is impossible to overstate the

benign influence of the weights and measures activity on social order. In an era where alienation from government is ram- pant, the citizen can see, if only by the

seals on the scales in the supermarket and

on the gas pumps, that his local government is protecting his interests.

The rest of the system impacts only

lightly on the citizen. He does have an interest in the health services delivery

system and his spokesmen are expressing

a legitimate concern over the adequacy of

the laboratory work. These tests, upon

which a great deal of diagnosis is based,

depend on elaborate automatic volume mea- suring equipment whose accuracy is largely unproved. Efforts are now under way

to examine this part of the system.

A second social impact which influences

measurements relates to inflexibility of

large bureaucratic structures which are designed to address certain specific

37

problems. Such structures are generally

established on the basis of a set of

conditions at some point in time. Continually changing technology, marketing

procedures and the like may result in more effective ways to achieve the desired result, or may make obsolete the

problems which originally established the

bureaucracy. In these cases, the advantages of changing the system must be com- pared with the disadvantages associated

with disrupting the work force. Generally,

if the measurements are not vital and if

the costs are accepted as a part of business, the work force is preserved. Because

mass, volume and density measurements are

so widely used, and because the measure- ment techniques are not difficult, there

are a number of areas where present practices are continued as the result of a social decision rather than a technological

one.

3.2 Status and Trends of the System

The precision of measurement has now reached a point where the ability to transfer the unit to other objects is limited by

the characteristics of the defining artifact and the characteristics of the weighing environment. The longevity of the

present defining artifact is contingent

on the resolution of these problems. In terms of the national measurement system,

the questions are largely academic.

One cannot seriously doubt that the

national measurement system is producing

results adequate for the requirements as perceived. Problems which are brought to NBS are seldom associated with the ability

to measure but with (A) inadequate definition of the measurement requirement

relative to the task at hand and (B) inadequate understanding of the measurement

process details. These problems are equally prevalent in science, industry and commerce. For modest measurement requirements,

these factors do not necessarily affect the

adequacy of the result relative to its

intended use. The efficiency of the measurement effort, however, decreases significantly, e.g. more measurement effort

is expended than the task requires, or measurements are made which are unrelated

to the basic task.

The parts of the system which are satisfied with the measurement results

currently obtained are essentially static.

In many cases, there is little motivation

for change. Where measurements are reasonably important relative to the task at hand

the trend is to eliminate or at least

reduce operator judgment, e.g. digital
indications, sometimes with computer interfacing, and completely automated processes

such as in the packaging industry.

One factor which will influence the

direction of the system is the politicaleconomic pressures for increased governmental intervention in the area of

standardization and enforcement of standards. These forces, typified by the

International Organization for Legal

Metrology, would bring a very large fraction of the measurement system under

surveillance. The legalization of

measurement has two basic limitations. In those situations where adequate results

cannot be obtained by "legal" means, the

system will have to be circumvented. The

laboratories supporting legal metrology

(e.g. state weights and measures offices)

cannot provide guidance without getting

into a conflict-of-interest situation.

That is, the regulator cannot provide

measurement guidance without assuming

responsibility for the adequacy of the

result if, at some later time, he must

pass judgment on the legality of the

resulting measurement process.

4. SURVEY OF NIBS SERVICES

4.1 The Past

A brief history of the Mass and Volume

Section is presented in Appendix B. For a discussion of the past NBS services in the

area of mass, volume and density measurements, there are two time periods of importance, one extending from the establishment

of NBS to approximately 1960, and one from

1960 to the present. In the earlier period,

services provided were essentially calibration of weights for manufacturers, and for

the states' weights and measures organizations. A considerable effort was made in

the formulation of specifications for mass

standards. A quasi -regulatory function was generated by limiting items acceptable for

calibration to those which complied with

the specification. These specifications

reflected the metrologist view of "what the user should have" rather than a careful

assessment of what was actually needed.

Work in the latter part of the period,

i.e. studies of the response of a balance to thermal air currents, the development of a 50 lb balance for the states' laboratories,

and the initial work on high precision kilogram balances, was instrumental in causing

the change in service provided. Typical

of this era was the acceptance of the

validity of a measurement based on the

reputation of the person who made the measurement and, in the interest of not being

38

wrong, error estimates were conservative.

This was also a period in which the charges

for calibration were not retained by NBS,

but returned to the Treasury. As a con- sequence, calibration was routinized with

frequent waiver of fees on the basis of

need. There was essentially no communication between NBS and the ultimate user of

the calibrated items.

The latter era started with the general

acceptance of the then new constant load

single pan balance. This gave the user a precision of measurement equal to, and in some cases better than, that available at

NBS. Conservative individual estimates of

the area of doubt associated with calibration results were no longer acceptable.

This in essence, forced a re-evaluation of

the services provided by NBS.

Changes in services evolved around the

idea that in a given facility, a measure- ment process is essentially a production

process. While the objects after

measurement and the results pass on to others, the measurement process remains and

in a sense is a capital investment. One

can utilize statistical techniques to evaluate the process, and to establish quantitative parameters which describe its

performance. These parameters are the basis

for realistic uncertainty statements and in

turn are the basis for judgments concerning

the adequacy of the results relative to the

intended usage, the need for process improvement, and perhaps most important, provide a means to monitor the performance of

the process independent of individual

judgments.

In the 1960's methods and procedures were

developed in accordance with the "new approach" for all of the calibration

services provided. The most completely

developed system is in the area of mass mea- surement with extension into a number of

measurement facilities through the Mass Measurement Assurance Program. The next most

developed system is in the area of capacity

standards, primarily to bring the NBS pro- cesses into a state of control and to extend

the techniques into the area of application.

In the area of hydrometer calibration and

the calibration of volumetric glassware,

measurement methods were developed incorporating the desired features but little was done to incorporate the methods into the

calibration procedures. In these areas the

calibration work load is small, and the new procedures were substantially different from

current practices. It was felt that the new procedures would not really benefit the users of hydrometers or volumetric glassware.
4.2 The Present--Scope of NBS Services

The variety of services available from

NBS which support the National Measurement

System range from providing access to the mass unit and the calibration of appropriate artifacts, to providing guidance to that section of the system associated with

"equity in the marketplace" and to providing consultation to all who ask for assistance. The calibration services of the

Mass and Volume Section, and the relation

between the Office of Weights and Measures

and the National Conference of Weights and

Measures are the services most widely

recognized and easiest to characterize in

terms of services provided and user

clientele. The consultation services,

supported in part by NBS funding, and by

"other agency" funding, are the most

difficult to characterize. Consultations

range from informal conversations relative

to selection of equipment, procedural difficulties, and problem definition, process

design, development of procedures and the

refinement of reference data. The following sections cover the direct services

provided by NBS. The indirect, or con- sultation services, are described in

4.3.2

4.2.1 Description of NBS Services

There are two organizations within NBS

which contribute to the measurement system.

The Mass and Volume Section is particularly careful about the interface with the users of the calibration services. In most

cases and particularly in the case of new users, each user is contacted by telephone

to determine what is needed and when. The

conversation is acknowledged by a formal

document stating the estimated delivery

date, the approximate cost, and special

requirements, if any. There are no clearly identifiable

organizational units within the section.

While some staff members are more knowledgeable in some areas than others, most can do

any of the tasks that the section performs,

subject to limitations due to the physical

strength necessary to handle some of the

larger equipment.

The calibration activities of the Mass

and Volume Section offer the following

services essentially "at cost" to the user:

4.2.1.1 Mass Measurement

(1) For those who desire to do the calibration of subdivision or multiples of the unit

themselves, NBS will establish mass values

for suitable pairs of starting standards,

e.g., kilograms or pounds, with uncertainties

commensurate with the requirement, and limited only by the amount of effort and the

uncertainty of the reference kilograms, Nl or N2.

(2) For those who do not have the facilities

or for some other reason do not elect to do

their own "work downs" or "build ups," NBS

will calibrate ordered sets of weights from

30 kg or 50 1 b to 1 mg or the appropriate

equivalent. Weights less than 1 mg require

special balances (quartz fiber) and handling

techniques (working in the field of a microscope) and a continuous maintenance of both

skill and equipment which cannot be economically done at NBS. Where such weights

are required, e.g., for work with small

quantities of short life isotopes, the NBS

will calibrate suitable "starting standards"

as in (1) above, and suggest suitable

procedures for "working down" at the user's

faci li ty.

(3) NBS will assign mass values and in some cases adjust to specified nominal values, to large objects from 50 1 b to 50 000 lb. (The

adjustment to nominal value is with reference to force machines, and the requirement

that the suspended weight exert a specified

force in a given gravimetric field.) The

adjustment of large weights is a matter of

convenience, considering the handling problems and shipping costs. NBS will not nor- mally adjust weights below 50 lb.

(4) The section will assign mass values and

associated uncertainties to any object from

1 mg to 1 kg, provided that the object is

sufficiently stable in mass to warrant the

measurement, and provided that the displacement volume is such that the object can be

handled with existing equipment.

(5) The section will make weighings of

convenience on any object up to 50 lb or

30 kg at no charge provided that there is no reasonable alternate source.

(6) Where repetitive measurements are required by other staff members, the section

will instruct, and supervise measurements

made by others on section equipment.

4.2.1.2 Volumetric Measurements—Glassware

(1) The section will calibrate the standard

items of volumetric glassware, made in ac- cordance with the GSA specifications, under

the provision that the requirements of the

specific work demands such a calibration.

The user is advised that the calibration

applies only to fluids similar in character

to water.

(2) The section will, on occasion, assist

large agencies, e.g., Food and Drug Administration, in monitoring the quality of the

products purchased by testing samples chosen
at random from a given lot. The agency

makes the decision regarding the disposition

of the lot in accordance with the rules in

the GSA specifications.

(3) The section will accept lots of pipets

which are used by the manufacturer in the

maintenance of a quality control system.

(One method of testing such a system is to put a "known" pipet in the inspection line

with the "unknowns.")

4.2.1.3 Metal Volumetric Standards

(1) The section will determine the contained

or delivered volume, and calibrate the indicating scale on all standard size provers.

The section will not normally adjust, or

seal, the location of the reading scale with

respect to the prover body. These items go directly to the user, with no intermediate

steps. The user in turn makes an effort to monitor the consistency of the section's

work.

(2) The section will calibrate .1 and 1 cubic foot bottles, which also go dir..

' 1 to the user.

(3) The section will calibrate slicke ju

standards. Adjustment, if required, must be

done by the manufacturer.

(4) The section will conduct a standardizing

test, and adjust as necessary, Stillman

standards, e.g., bell provers of 1 cubic

foot capacity. This is currently done with

a single purpose test apparatus, and gradual

decrease of requests does not warrant further refinement. (Most items of this type

are calibrated by "strapping," e.g., determining the displacement volume from direct

linear measurement.)

(5) The section will calibrate either to contain or to deliver, any metal container

provided that it is sufficiently rigid to be handled in the filled condition, that it can be leveled, and that the end point is

sufficiently well defined to warrant the

calibration; and further, provided that the

effort is necessary to the manner in which

the vessel will be used. (This is of course

limited by the capacity of the existing

equipment.

)

(6) The section will accept tests of various

apparatus provided that the results of the

test are not proprietary, and subject to the

condition that the results will benefit a large number of users.

4.2.1.4 Density Measurements

(1) The section will accept hydrometers for

calibration which are of such quality, both

in manufacture and precision, to warrant the

calibration effort, and provided that the

items will be used as manufacturers' standards, or directly by the user. The section

will not accept certain types of hydrometers

where the hydrometer scale is not directly

related, or relatable, to density, e.g.,

lactometers.

(2) The section will calibrate solid density

standards for use in specific measurements.

(3) The section will determine, or consult

with, or assist, in the construction of

apparatus for determining the density of

a wide variety of small objects, e.g.,

gradient columns, special floats and the

like.

(4) The section will determine the density

of fluids within the capabilities of the

existing equipment, and provided that the

fluids do not require special handling procedures beyond that available in the normal

1 aboratory

.

4.2.1.5 Mass Measurement Assurance Program

The Measurement Assurance Program, as operated by the section, has not been sold

in an aggressive manner. Participation is

voluntary, and prior to making the decision,

the prospective participant is told quite

clearly that it requires a lot of work. If on the basis of his analysis he requires

either (1) the maximum performance of his

measurement processes to satisfy the re- quirements of his specific task, or (2) the

benefits in the form of reduced measurement

effort by virtue of the quantitative knowledge of descriptors of his measurement process, he is then encouraged to participate.

Approximately six months is required to make

the MAP operational in the normal mass mea- surement facility. Beyond that, the frequency of usage is up to him. If he has the

necessary supporting facilities, he may

elect to run the program himself with only

minimal connection with the section. In other cases, the section may provide all of

the supporting effort. Periodically, the

knowledge of his process performance parameters is updated. (At this time all of the

present participants have been updated at

least once.) Currently some of the users

are hierarchy laboratories, others are in

support of certain direct measurement

requirements. Some do almost everything

themselves, and others rely on the section

for continuous support.

4.2.1.6 Office of Weights and Measures

The second operational unit is the Office

of Weights and Measures. The role of OWM is to provide leadership and those technical resources that will assure accuracy of the

quantities and quantity representations in

all commercial transactions for all buyers

40
and sellers in the United States, and to promote a uniform national weights and measures system.

In fulfilling its mission, the Office of

Weights and Measures engages in a wide range

of activities all of which are essentially

funded by NBS. Foremost is the assistance

offered to the States in the following

areas:

Laws and Regulations : The development of model weights and measures laws and technical regulations

for the States and local jurisdictions.

The evaluation and updating of laws and

regulations at the request of the States.

Standards and Laboratories : The development and dissemination of

design and performance specifications for

capacity for use as State and local ref- erence, laboratory, and field standards,

and the encouragement of manufacturers

to make available standards that conform

to such specifications. The conduct of

the New State Standards Project, which

provides for the issuance of new laboratory standards and instruments and

modernization of State weights and measures laboratories. Consultation and

recommendations on laboratory facilities,

organization, instruments, and technical

procedures. The calibration of secondary

standards for the States and industry.

Testing and Equipment and Procedures : The design of testing equipment and the

development of testing procedures for

weighing and measuring devices.

The conduct of the master railway track

scale test project and the testing of

commercial track scales operated by the

railroads and other industries located

throughout the nation.

Measurement Studies : The identification, analysis, and

solution of technical problems in the

measurement area of commerce.

The study, including field investigations, of weighing and measuring equipment, the preparation of specifications

and performance tolerances, and the es- tablishment of standard practices involving the use of such equipment.

The examination of prototype commercial

weighing and measuring devices and equipment submitted by manufacturers for con- formance with National Bureau of

Standards requirements.

Packaging Practices : Market surveying to determine the

weights, measures, and quantities in

which commodities are packaged for retail

sale, and the extent to which voluntary

product standards are being adhered to by

industry.

Determining the relationship between num- bers of package quantities available at

retail and its effect on consumer ability

to make a value comparison.

Distributing published standards and regulations resulting from the Fair Packaging and Labeling Act, providing information and assistance to State officials,

and generally promoting uniformity in

Federal and State regulation of the labeling of packaged consumer commodities.

Providing advice and counsel to the packaging industry on means and methods for

achieving the aims of the Fair Packaging

and Label i ng Act. Technical Training

The conduct of formal and informal technical training sessions for weights and measures officials, laboratory technologists, and industry representatives.

Information Dissemination : The preparation and dissemination, in

conveniently usable form, of data on weights and measures units, systems, and

equivalents, to satisfy the particular

needs of the Federal Government, State

and local governments, educational institutions, business and industry, and

the general public, including the development and maintenance of archival and

reference collections of published

material

.

The development, the preparation, the

publication, and the dissemination of appropriate information on standards, testing equipment, technical procedures,

technical investigations, and standard

practices.

Conferences and Meetings : The plan and conduct of an annual National Conference on Weights and Measures,

including all secretariat functions to

the Conference and its standing

committees.

4.2.2 Users of NBS Services

The principal user community of the Office of Weights and Measures is the State

and local weights and measures officials.

A small, but important, additional service

of this NBS group is their prototype

approval program. This program allows

manufacturers of measuring devices used in

trade to obtain approval certifying that

the device satisfies the requirements of

Handbook 44. Such certification is ac- cepted by many jurisdictions in lieu of

41
their own inspection. The program is small

(about 40 inspections per year) but growing.

The Mass and Volume Section, on the other

hand, has a much more diffuse clientele. The

most serious customers are those who subscribe to our Measurement Assurance Program (MAP). There are currently 18 facilities participating in the MAP program.

The nonclientele group contains all of

those whose measurements are now adequate

for the intended purpose, or at least

thought to be by the user.

In order to establish a profile for the users of NBS services, the customers over a four-year period were categorized according

to nature of their business using the Standard Industrial Classification (SIC) codes.

While it was not possible to categorize all

of the customers according to this method

of classification (87% for Mass, 67% for

Volume, and 61% for density), Figures 5 through 8 show the frequency of re- quests from various categories over the

period of the study.

4.2.3 Alternate Sources

Technically the user's decision to accept

or reject an alternate source for calibration should be based on the uncertainty of

the calibration relative to the task at hand. Generally, if the user's process

cannot detect the small differences between

like objects which are clearly identifiable

in the calibration process, the user cannot

utilize the full benefits of the calibration. Practically, many decisions with re- gard to source of calibration are based on political or economic factors rather than

technical requirements.

With access to the defining unit, and

with the world's most precise balance,

NBS-2, BIPM provides the highest level calibrations. The uncertainty of the results

are limited by the instability of the

defining artifact. BIPM has provided calibrations for selected artifacts to be used

in redefining certain electrical units,

i.e. the ampere and the faraday. BIPM has

provided calibration services at the kilogram level for at least one foreign balance

manufacturer. While BIPM is not in a position to provide general access to the defining artifact, the precedent has been

established with regard to providing support

for certain types of activities.

While all national laboratories are acceptable alternate sources for calibrations with regard to military specifications, most national laboratories limit

their services to organizations within the

territorial boundaries of their governments.

On occasion users may obtain calibrations

42

from other national laboratories using local

organizations as "fronts." In the area of mass measurements the results are used as "informal international audits" rather than sources of calibration.

The higher order calibrations provided by

NBS reflect the uncertainties from three

separate measurement processes, the defining

artifact to the prototype kilograms,

the prototype kilograms to the ni chrome

kilograms, and the ni chrome kilograms to the

artifacts being calibrated. Of these three

processes only the latter has been completely characterized. With the exception of a small group of measurements

which were made when NBS-2 was still at NBS,

essentially no calibrations have been made

relative to the prototype kilograms. This

has primarily been due to a lack of equipment and to uncertainties associated with

the air density algorithm. Present calibrations are on the basis that the historical

values assigned to the nichrome kilograms

are exact. The uncertainties assigned to the various

pairs of kilograms of the Mass Measurement

Assurance Program participants are on this basis, thus these laboratories are capable of providing an alternate source

for most of their requirements which formerly were sent to NBS, as well as for

others if they desire. (An "informal

international audit" shows that the

practical mass scale as disseminated by NPL and by NBS may be offset by one part

in ten million. This is attributed to

problems associated with the air density

algorithm.) Since the consistency of the

work of each of these laboratories has

been evaluated both relative to NBS and

relative to other participating laboratories, one or more could function as an interim calibration source in the event

of disaster at NBS. The maintenance of

such service is important, not from the

standpoint of providing calibrated weights

which are in turn used to calibrate other

weights, but because wel 1 -cal ibrated artifacts are needed to characterize modern

weighing devices and measurement processes.

With the completion of current

activities directed toward the development

of equipment and procedures and the evaluation of the air density algorithms, it is

planned to re-calibrate these pairs of

kilograms relative to the prototype

ki 1 ograms.

Perhaps the most widely available calibration procedure is that associated with

establishing compliance with adjustment

tolerances. Here the user's choice of source may be either practical or economical or both. The state laboratories and
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44
the weight and balance manufacturers provide calibration services complete with

proper evidence for compliance with

"traceabi 1 ity" requirements. Many former

users of the NBS services now utilize these

sources with substantial economic savings.

(Some states provide such services at no cost.) In some cases NIBS calibration

services are used for this purpose, i.e.

the NBS assigned values are compared with

the adjustment tolerance limits to verify

compliance, and the limitation on the use

is then set by the tolerance class rather

than the uncertainty of the value. In •these cases the decision is political

rather than economic, i.e. use the NBS

calibration services in lieu of justifying

an alternate source. There are no technical reasons to support the NBS calibrations in the areas of

volume and density measurements. The

methods used at NBS are well documented and

widely disseminated. Adequate equipment is

generally available in the user's facility.

However, with the exception of IRS (hydrometers) and FDA (glassware) previously mentioned, attempts to develop alternate

sources have not been successful. The reasons for this are somewhat complex. In the case of the small user, i.e. a hospital laboratory, the practice of self-calibration

diverts resources from the primary mission

of the laboratory. Further, such practice

raises the question of defense in the case

of challenge by those who make judgments

based on the measurement output of the

laboratory.

For large uses, i.e. the petroleum industry (volumetric process), the alcohol and

sugar industry (hydrometers) there appear to be two reasons, both associated with the

interface between the producers and users of

measurement data. One is the need for a consistent defensible reference. The second

is the widespread belief that where large

amounts of money are involved, measurement

data will always be biased in the favor of

the organization which has produced the

data . In such an environment the need

for unbiased "third party" calibrations is

essential

.

4.2.4 Funding Sources for NBS Services

The two NBS organizations which are administratively separate have different

funding patterns.

The Mass and Volume Section profile, both

for funding and staff, is shown below.

Staff Funding ($1000)

Reimbursabl

e

Yr Total Prof NBS Work Total

1970 21 6 300 160 460

1971 17 6 325 165 490

1972 17 7 380 no 490

1973 9 2 210 60 270

1974 10 3 205 35 240

The large change between 1972 and 1973 was

the result of the establishment of the

Dimensional Technology Section. The work of

maintaining and characterizing the measurement processes of NBS, and general support

to the appropriate segments of the national

measurement system, accounts for most of the

work and is funded directly by NBS. Measurements which are done for others are, in

most cases, charged on the basis of "at cost.

The staff profile of the section does not reflect the utilization of the services

provided by both the Office of Measurement

Services and by the Statistical Engineering

Laboratory. In both cases, many of the

respective staff members are considered as "ex officio" members of the Mass and Volume

Section.

The Office of Weights and Measures

operates under a total budget of just under

$450,000 with a staff of 18.

4.2.5 Mechanisms for Supplying Services

Access to the unit is provided through

the calibration services. The transfer

mechanism is the Report of Calibration which

is returned to the submitter along with the

calibrated items. In the case of mass calibrations the report is essentially a com- puter prepared "laboratory notebook" which

not only gives the results of the calibrations in several different forms, but also

completely delineates the details of the

measurements which were made and the status

of the performance of the measurement pro- cesses used. All calibration reports show

the conditions under which the results

apply, as well as realistic certainty statements which permit the user to evaluate the

results relative to his requirements. In some instances, where there is a history of

NBS calibration of certain items, the previous history is taken into account in the

assignment of value, and associated

uncertai nty

.

TT5 There is a published strategy for

biasing measurement data where disagreements are resolved by NBS mea- surement with the party having the

greatest discrepancy with the NBS

paying the cost for the referee

measurement.

45
The documentation associated with the

Mass Measurement Assurance Program includes

the calibration of the participant's standards, the characterization of the participant's process based on measurement data

from his facility, a verification of the

consistency of the results through independent calibrations of an arbitrarily selected

set of weights by both the participant and

NBS. In addition, the participant is provided with control chart data which will

permit a continuous monitoring of his process performance. Follow-up documentation

may include recalibration of his standards

at NBS, recalibration of his standards in

his facility relative to furnished NBS

standards, a re-evaluation of the consistency of measurement between his facility

and NBS, and finally, an occasional "update"

of pertinent parameters for his process.

Detailed access to measurement methods

and procedures is provided through the generation of a literature base, and through

consultation. The literature base consists

of a series of publications ranging from

"OVERLAP," an irregular news letter to MAP

participants, to NBS reports, Technical

Notes, Monographs and formal publications in

journals such as "Metrologi a. " For the most

part method and procedures are covered in

detail in NBS reports. The intent, in general, is to provide a depth of detail sufficient to not only permit the interested

user to make the measurement, but also to

permit him to assess the uncertainty of his

result. The methods presented can be simplified as appropriate to his requirements,

or to the requirements addressed by

voluntary standards groups.

Tutorial assistance has been provided

through participation in seminars conducted

by the Mass and Volume Section, and by the

Office of Measurement Services. On occasion

invited talks have been presented at various

society conferences, including the National

Conference of Standards Laboratories, the

IEEE, the American Defense Preparedness

Association (formerly the American Ordnance

Association), the Aerospace Industries

Association, and others. The most effective

access to methods and procedure, however, is

direct consultation relative to a particular

measurement requirement. These consultations

range from inquiries concerning the availability of appropriate standards to system

problems concerning the health and welfare

of the nation (e.g. determining the amount

of coal dust in mines, and the costing of

measurement in laboratories of the Food and

Drug Administration) and large segments of

the national economy (e.g. bulk measurements

of petroleum and nuclear materials).

The Office of Weights and Measures,

acting as the secretariat of the National

Conference of Weights and Measures, provides

both administrative and technological ser- vices to that organization and its various

study committees. OWM provides a calibration service to the state laboratories for

items which are not designated "primary"

standards. The items include trailer

mounted provers used to test a variety of

tanks and metering devices, large weights

used for testing large capacity scales,

miscellaneous glassware items used for

testing liquid packaging containers, and

the like. OWM conducts extensive training

operations for all levels of personnel

within the state weights and measures organizations. OWM also operates a program designed to verify the consistency of mass measurement in the various state laboratories. OWM operates, on an intermittent

basis, the railway track scale test cars which provide a means for calibrating railway master scales, and such other privately owned scales as arranged for in the course of planning the itinerary for the

two test cars.

4.3 Impact of NBS Services

4.3.1 Economic Impact of Major User

Classes

The user classes, discussed in

Section 4.2.2, show a degree of commonality

between the three areas of measurement.

This in turn suggests that there may also

be a commonality between all of the users

of the NBS calibration services in all measurement areas. In considering impact, it seems important to identify this commonality in order to differentiate between the users who are in essence "told" to use NBS

(e.g., by contractual requirements) and

those who use NBS calibration services as

a matter of need or convenience. This is

not to imply that those who are "told" to

use NBS would not normally come to NBS

anyway, but rather to differentiate between

realistic calibration needs and the artificial needs generated within the

i nf rastructure.

Table 8 is a summary of all of the users

of all NBS calibration services, by dollar

volume, and by number of facilities served

for fiscal year 1975. The military con- tractor category of the private sector includes 70 corporations which account for in excess of 87% of military research, development, test and evaluation contracts

($5,474 billion); 46 of these 70 corporations, which account for 50.9% of the

RDT&E contracts, are large industrials

46
(Fortune's "Top 500"). The total industrial

sales of these 46 (1974) is $129,463 billion, thus the military business is only

about 2.5% of their total effort. Further,

the total sales of these 46 represent only

about 15.5% of the total sales of the "Top

500" ($833,956 billion or 59.3% of the

1974 GNP, $1,406.9 billion).

Table 9 Survey of Users of All NBS

Calibration Services (1975)

No. of

Cost of Facilities

Calib Served

Total Government $ 542,812 63

Dept of

Defense $ 486,085 (89.5%) (35)

OTHER 56,727 (10.5%) (28)

Total Private $1 ,234,844

Military Contractors $ 615,050 (49.8%)

OTHER

Overal

1

$ 619,794 (50.8%)

$1 ,777,656

NCSL Membership $1 ,157,862 ( 65%)

Non-NCSL $ 225,910 (12.7%)

(accounts over

$5,000)

OTHER $ 393,884 (22.3%)

871

(224)

(647)

934

(238)

(18)

(678)

(Average cost/user $580)

The National Conference of Standards

Laboratories is a non-profit, laboratoryoriented organization which promotes co- operative efforts toward solving common

problems faced by standards laboratories in

their organization and operation. With few

exceptions the membership is comprised of

government laboratories supporting hierarchy chains of calibration laboratories,

and organizations which must interface with

contractual requirements imposed by governmental agencies, primarily the Department

of Defense. The membership, which is not

generally end-use oriented, accounts for

65% of the total NBS calibration effort.

Non-NCSL members with accounts over

$5000, of which approximately 50% of

the $225,910 is associated with the

calibration of products from less than 10

instrument manufacturers, accounts for

12.7% of the NBS effort. For the

remainder, 22.3%, the average cost per

facility, for 678 facilities, is slightly

less than $600. An unidentified number

of the facilities in this group are subcontractors which are required to "maintain" certain measurement capabilities, and, on occasion, items submitted

for periodic recal i bration have been

received in the same unopened package

which was used to ship the items after the

previous calibration.

The above summary of the users of NBS

calibrations is descriptive of the users of mass, volume and density calibrations. The

impact of the NBS services is the degree to

which these services benefit the user in

attaining measurements adequate for his

needs, either realistic or imagined (e.g.,

established by a bureaucratic infrastructure). The degree to which direct services

are required is the ratio of an acceptable

uncertainty of the results from the user's

process, under actual conditions of use, to

the uncertainty of the NBS calibration mea- surements. For example, the ratio of the

uncertainty of the internal balance weights

of one balance manufacturer who is a participant in Mass MAP, to the uncertainty of

the NBS calibration is on the order of 1.5 to 2, obviously requiring direct contact.

As a result, the dissemination of the mass

unit as embodied in stainless steel is

widely available with little degradation.

On the other hand, the same ratio for

acceptable commercial weights ranges from

100 to 1000, thus adequate services are available from many sources and those who

insist on NBS calibration are merely buying

a name. Generally speaking, there are very

few uses of mass, volume, and density

calibrations with requirements commensurate

with the uncertainty of the calibration

resul ts. In contrast, the consultative activities,

from short telephone discussions to

long term continuing studies are directly

related to specific measurement requirements or measurement assurance requirements. Two such long-term activities are related to the nuclear power industry and

the petroleum industry.

In the nuclear power industry, the first

quantitative measure of the amount of material in a "spent" reactor core occurs after

the core material has been dissolved from

47
its cladding. The amount of material is

determined from assaying samples drawn from

a tank of "known" volume. The result not only establishes the monetary value of the

material, but also establishes the base for

material accountability under the nuclear

safeguards program. The Mass and Volume

Section has developed and documented measurement techniques for determining the

contained volume of large tanks. Working

with voluntary standards groups, the techniques are being incorporated in standards

which will become industry standards. This

type of measurement support activities at 3 U.S. government reprocessing facilities which

handle material used by the military. Should

commercial reprocessing activities be au- thorized for the U.S. the section's activities in this area would support that

effort. The projected value of the re- sultant electric generating capacity for

1985 from reprocessed fuel is in excess of

$5 billion. Should the plutonium fuel cycle

be used then tank volume measurements be- come critical for accountability and safeguards purposes.

The Mass and Volume Section supports the

petroleum industry in three ways: the calibration of large volumetric provers which

are used worldwide to test metering devices;

the calibration of hydrometers, density

being an important parameter in processing

and application; and currently the American

Petroleum Institute/NBS Physical Properties

Project. An estimate of the worldwide com- mitment to petroleum measurement is shown

in table 9. The average "barrel" is measured twelve

times with numerous custody changes between

the well head and the ultimate user of the

finished product. Shipper/receiver differences in terms of dollars are based on bulk

measurements of quantity, which in turn is

dependent on the properties of the material

being transferred. Measurement detail is a consensus decision establishing the basis

(e.g., NBS calibrated provers) and the extent to which systematic errors are minimized with respect to the cost of the

material and the cost and practicality of

measurement procedure. Attention to detail

is directly proportional to the cost of the

material

.

The worldwide pricing structure is based

upon the bulk volume and density at 60°F.

Since custody transfer takes place at tem- peratures differing from the standard temperature, computation of the volume at 60°

F

is done using the measured temperature and

the density at the time of transfer (e.g.,

as measured with a hydrometer), the

measured value as determined by a calibrated metering device, and a volume

reduction table accepted as an industry

standard. Discrepancies in the table are amplified when large temperature and density

changes occur in transit, e.g. on-loading

in the middle East; and off-loading at a North Atlantic port.

The current volume reduction table is

based on thermal expansion coefficients and

densities of North American crude oils and

products prepared by NBS around 1915. In 1973 production from North American fields

had dropped to 25% of the total production.

It has been known for some time that the

table does not reflect the characteristics

of presently marketed crudes, however, the error relative to the cost of the material

was considered acceptable. At the current

price for imported crude oil, a .16% error

over a temperature differential of approximately 40°F represents an inventory loss in

transit of $5 million per month at the current import rate of 8 million barrels/day.

The joint NBS/API activity is to characterize both crude and products on a worldwide

basis (67% of 1975's proven reserves). This

data will be the basis for a consumer's

decision relative to both the method for

reducing values to a common basis and the

measurement detail associated with determining the appropriate parameters.

4.3.2 Technological Impact of Services

Historically, NBS impacted the weight

manufacturing industry through its technical

publications such as Circular #3 and 547.

The tolerance classes set up in these

documents are widely accepted.

The impact on the precision balance

industry has been less profound due perhaps

in large part to the fact that this

industry is largely European based. However, at the 2500 lb level the "Russell"

balance, named after a Bureau employee, is the standard of the nation. More recently,

the NBS-2 type of kilogram comparator, man- ufactured by a U.S. concern, has found a market among other national laboratories.

Commercial weighing devices manufactured

to conform to Handbook 44 also reflect NBS

thinking.

With respect to volume standards, the

NBS role has been less innovative, but the

methods of calibration throughout the

industry owe a great debt to NBS. The

continuing calibration effort, although

small, provides the unifying tie point

for a sizable, but diffuse, industry.

The impact on the makers of density

measuring equipment has been of yet another

kind. In this case, the detailed technological base of density measurement was developed at NBS. The proper configuration,

48
Table 9 PETROLEUM MEASUREMENT COMMITMENT

Crude Finished

Comroi tment Petrol eum Products Total

Measurement $800,000,000 $2,000,000,000 $2,800,000,000

Facili ty

Investment

Equivalent 22,500 27,500 50,000

Ful 1 -Time

Personnel

Measurement 255,000 395,000 650,000

Poi nts*

Frequency "Average" Barrel Measured 12

Cost of 0.5% Measurement Error Per 1000

Barrels Petroleum at $13.00 Per Barrel $65.00

Monitoring discrepancy per day at cur- rent import rate $500,000.00

*Tanks, pipelines (meters), tankers, barges, tank cars and tank trucks

ESTIMATED WORLD-WIDE OIL INDUSTRY

INVESTMENT IN BULK PETROLEUM

LIQUID MEASUREMENT

methods of use and necessary precautions

are all spelled out in NBS technical

papers. The industry is based on these

principles.

At a higher level of accuracy, the NBS

techniques of hydrostatic weighing represent the "state-of-the-art" and are universally recognized as such. This work

continues with the silicon density work

previously mentioned.

NBS has a technological input to other

specification-preparing groups, both

government and private. For example, the

appropriate section of the NASA Mass Properties Manual were prepared by the section.

Procedures and statistical methods prepared

by the section have been incorporated in

various published API procedures. Where

possible the section has taken the initiative to see that the procedures are appropriate for the task, that the user understands what he is supposed to do, and

that the equipment furnished will indeed

do the job.

The section staff members are consultants

to the Institute of Nuclear Materials Management (INMM) Writing Group 8 and subgroups

thereof which have the task of preparing

specifications or guides for the measurement

of nuclear materials in cooperation with

ANSI. The specifications in preparation are:

(1) ANSI Nl 5.18 "Mass Calibration Techniques

for Nuclear Materials Control"

(2) ANSI NT 5.1 9 "Volume Calibration for

Nuclear Materials Control"

The above standards, when accepted and

formally approved in accordance with ANSI

procedures, will no doubt be made mandatory

by NRC (Nuclear Regulatory Commission) in

the nuclear industry.

The staff has participated in the work of

ASTM subcommittee El 8, Hydrometer Subcommittee. In early 1974, the parent committee,

El, on Methods of Testing, elected to disband itself. The subcommittee El 8 has been

redesignated El .05, under a different parent

committee. The section will continue to be

a part of this committee because of the

49
strong reliance of the industry on artifact

standards.

The National Conference on Weights and

Measures had its beginning in 1905, when

the Director of the National Bureau of

Standards called a meeting of representatives from the several States

"to bring about uniformity in the State

laws referring to weights and measures,

and also to effect a close cooperation

between the State inspection services

and the National Bureau of Standards."

From an initial attendance of 11 persons,

the Conference has grown until now it

brings together at its meetings a total of

approximately 500 persons comprising

weights and measures officers, other officials of the Federal, State, and local

governments, and representatives of equipment manufacturers, industry, business, and

consumers. The Conference develops many

technical and general recommendations in

the field of weights and measures administration, and its programs explore the

entire area of this economically important

segment of governmental regulatory service.

The participation is in national and

international activities in the fields of

weights and measures standards and practical metrology. Such participation

includes:

(a) the development of and negotiation

toward the adoption of both national and

international specifications in the

assigned area;

(b) correspondence and other communication

with experts of the United States and of

other nations;

(c) technical committee activities;

(d) attendance at and participation in

appropriate meetings and conferences of

the Federal and State Governments and of

regional groups, business, industry, and

educational institutions.

4.3.3 Pay-off from Changes in NBS Services

Substantive changes resulted from two

factors; one, a concentrated effort in the

early 1960's to completely characterize the mass measurement processes at NBS, and two,

the recognition of measurement as a production process whose product (measurement

results) should be evaluated relative to the

end use rather than relative to state-ofthe-art measurement capabilities, e.g. the

"best" measurement process is one which

produces adequate results in the most

economical manner. As a result of the first

effort, the basis for judgment concerning

the adequacy of a measurement was changed

from operator opinion to quantitative tests

relative to pertinent process performance

parameters. For the first time realistic

uncertainty statements, based on demonstrative evidence, permitted unbiased comparison

of measurement results from different mea- surement processes. Realistic uncertainty

statements, in turn, permitted an assessment

of measurement process detail relative to end use requirements.

The techniques were extended to the field

by changes in reporting format, tutorial

training at NBS, and technical publications.

This effort permitted the development and

acceptance of alternate sources for routine

calibrations for both weight sets from 100 g down, and for volumetric glassware. Weight

manufacturers, utilizing adaptations of the

techniques used at NBS, were able to market

calibration services acceptable to a large

portion of the user community at a cost to the user substantively less than the cost

for NBS calibration. In the area of volumetric glassware, the Food and Drug Administration was the primary user of the NBS

calibration services, primarily to verify

compliance with specification tolerances.

NBS efforts devoted to the development and

acceptance of suitable specifications, to the verification that manufacturers' products did indeed meet these specifications

resulted in a change in the method of processing glassware. The agency now procures

glassware through the established procedures

of the General Services Administration with

a direct saving in excess of $150,000 per

year, the amount previously spent annually

for NBS calibrations.

The reduction in the number of calibrations for manufacturers and suppliers

opened a direct channel of communication

with people involved in operating measure- ment processes. As the characterization of

the NBS processes progressed responses to inquiries became objective rather than

subjective. Ultimately, the routine "fee

schedule" calibrations were replaced by "at cost" calibrations in which the calibration

effort was tailored to the particular cus- tomer's needs. The measurement assurance program concept was developed and augmented.

This concept has now been accepted in many

other areas of measurement. The concept is

used in the nuclear weapons industry to monitor the performance of the facilities

involved. As a direct result of this program, the section was asked to make an objective survey of the nuclear reprocessing

industry relative to mass and volume

measurements.

Continued efforts devoted to the characterization of measurement processes and the

development of measurement methods provided

direct support to accomplishments ranging

from the redetermination of Avagadro's

50
Number, to the resolution of litigation con- cerning the performance of a group of 30 kg

balances procurred by OWM for the new state

laboratories. Studies on the density of

single crystal silicon resulted in a "solid

object" density standard overcoming the limitations associated with water. Procedures

were developed and documented which would

provide a base for determining the volume of

large tanks in the nuclear industry.

Detailed analysis of the calibration user clientele and the way in which the users utilized the calibrated items were made. In many instances it was questionable as to whether the NBS calibration efforts had any

real impact on the quality of the work done

by the user. It was concluded that the

"catalog-fee schedule" invited commitments

of NBS facilities without prior discussions

concerning the adequacy of the effort relative to the particular task. Many requests

for calibrations were, and still are, required for compliance with various standards. It was decided that participation in the preparation of voluntary standards

should be limited to consulting rather than

direct participation. It was felt that as a consultant, NBS could aggressively increase

the span of input to the voluntary standards

procedures (see figure 3). In the case of

old, established standards, this has not always been successful. However in the development of voluntary standards for the

nuclear industry, NBS, acting as a consul

ant, has an effective input over the whole

span of the process, from the identification

and quantification of the requirements by

the regulation, to the development of

methods and techniques, the preparation of

the appropriate voluntary standard, the

demonstration of the adequacy of the standard, the acceptance of the standard by

the regulator, and the manner in which com- pliance with the standard will be judged.

The increased span mentioned above has

resulted in a fundamental change in the

scope of certain new voluntary standards in the nuclear industry. Traditional older

standards are essentially detail standards

specifying itemized equipment lists and

procedural steps; such standards, essentially without exception, ignore discussing

in detail the uncertainty of the result.

(It is presumed that adequacy relative to

a particular requirement has been con- sidered by the committee which prepared

the standard.) The new standards are performance standards, concentrating on the methods for assessing the performance

of existing processes relative to specified requirements. In a producer-consumer

relationship, this action gives the producer a freedom for choice and at the same

time, the consumer is assured that the

requirement is satisfied.

Perhaps the largest benefit from change

is the progress which has been made in

relating the ideas of Mach, Carnap,

Eisenhart, and others to modern measurement

processes. It is now possible to describe

most measurement processes in generalized

terms independent of process detail. This

permits a logical delineation of requirements relative to a particular task, which

in turn provides a list of the elements

which must be tested to establish that the

performance of that process is adequate for

the intended usage. As this work is refined

and disseminated, it will impact the design

and development of future measurement

systems. One of the encouraging factors

relating to this work is the ever increasing

number of people who are now aware that

there is something more to measurement than

possession of adequately blessed standards

and the blind following of a specified

procedure —people who can discuss in some

detail measurement processes, process

characteristics, and measurement requirements relative to an identified need of

importance in accomplishing a specific

task.

4.4 Evaluation of NBS Program

The two groups within NBS which support

the mass, volume and density system are organizationally separated with essentially unrelated missions. One group is concerned with the legality of measurement

and equity in the marketplace, particularly

in regard to consumer products. This group

is, in a sense, semi -regulatory . That is,

having created a system for control largely

based on visibility which has become a con- sensus system for the various states, this

group is mostly concerned with implementation of the system. The system controls a large segment of the instrumentation industry as well as the control measurements at the consumer level. Typical of all large consensus systems, it cannot respond rapidly to changes in technology. The ritualistic aspects of the effort tend to take

precedence over the efficiency of the effort and, in like manner, administrative

activities predominate. While the technological requirements of the system are not stringent, the lack of technological resources seriously limits the scope of

the programs.

The second group is concerned with the

adequacy of measurement throughout the

system. The constituency of this group is voluntary with one exception. As "keepers

of the kilogram" the group is a "servant
to all who desire, or are directed to establish, a direct traceability to the

unit." This group, in the early 1960's,

aggressively undertook a long-range plan

to change from merely being "keepers of the

kilogram" to becoming a center for measurement excellence in the areas of assigned

responsibilities. One of several goals was

that no current or future task should be

limited by the inability to make adequate

measurements. Through the mechanism of

characterizing the calibration processes,

the basis for measurement assurance was established, e.g. operationally verifiable

evidence that process performance is as expected. The efficiency of the measurement effort was addressed by emphasizing

that the "best" process was that which

produced adequate results with minimum

effort. Cooperative programs were es- tablished with other facilities to study

factors affecting the consistency of

measurement over time and over the

environmental conditions in which

measurements must be made.

By and large, the transition has been

successful. Measurement assurance relative to the transfer of the unit has been

adopted in several measurement areas. Even this, however, has not been without

difficulty, as illustrated by the various

National Academy of Sciences Evaluation

Panels.

In 1969, the evaluation panel

recommended: . . . extension of the Pilot

Program (now called the Measurement

Assurance Program) into the volume

calibration activity, specifically, and

into other NBS calibration activities,

generally . . . As the Measurement Assurance Program

was developing in the area of length

measurement, in 1970 the evaluation panel was divided in opinion to the point that

a minority evaluation was submitted. It was quite clear that NIBS had failed

miserably in presenting the intent of the

program.

In 1972, the panel "endorses" NBS

policies pointing to expansion of the MAP program, and in 1975, the panel report

states:

"The panel is extremely pleased to see the

progress which has been made in the Measurement Assurance Program in the Mass

and Volume and the Dimensional Technology Sections. We believe the measurement assurance approach will provide a more viable method of transferring standards from the National Bureau of Standards to commerce and industry by

placing a greater emphasis on measurement assurance and the error bands

associated with measurements and less

emphasis on attempting to transfer precise absolute measurements. Greater

confidence can be placed on the use of

the measurements and standards at lower

costs, both to The National Bureau of

Standards and to commerce and industry.

The panel believes there would be benefits in extending the assurance program

in the future to all dimensional

measurements.

Thus, over a six year time span, the

intent of the program was finally understood, at least with regard to the transfer of the unit. It would seem that more attention to the educational aspects of

the program would have considerably reduced

the friction and would have shortened the

time span between introduction and

acceptance.

With one exception, the measurement

assurance approach is not reflected in

voluntary standards. The exception is

with members of the Institute for Nuclear

Material Management who are incorporating

the approach in some of the voluntary

standards being prepared for the nuclear

industry. There may be several reasons for

this, one of which is the lack of aggressive or appropriate selling on the part of

NBS. Traditionally, voluntary standards

are consensus standards in which the preparing committee assumes the responsibility

for the adequacy of the specified procedure

and interpretation relative to a specific

task. Few if any such standards include error analysis or any discussion of methods

to assess the uncertainty of the result.

Individuals who constitute these committees, however, recognize that while such

standards may be necessary to order in the

marketplace, or in the simplification of

the exchange of data, the use of these

standards is not always sufficient relative to the task at hand. The resulting

standards tend to represent a minimal consensus relative to an interfacing problem

rather than realistic efforts at the point

of decision.

The above implies that if the benefits

of measurement assurance are to be realized

in industry, there must be a one-on-one

interaction at the point where the benefits

are real. With regard to NBS as a whole,

this is a null effort for two reasons; one obviously the futility of a one-on-one con- tact with everybody, and the second, the

absence of an identifiable measure of success. If a company should adopt measurement assurance procedures with any measure of success, and there have been

several which have seen fit to do so, the

fact is immediately privileged information.

52
It would seem inevitable that as the

constituency grows, the philosophy would

become identifiable in future voluntary

standards. Such an effort is a long,

slow process, as is any worthwhile reform,

with periods far longer than the normal

budgetary cycle.

With regard to other aspects of the

program of the latter group, the range of

activities has increased greatly over the

past 15 years. "Customized" at-cost calibration services are furnished in all

measurement areas. There are active

efforts with tangible results ranging

from the development of precise research

weighing devices and the study of air

density as it relates to mass measurement

to development and tutorial efforts con- cerning bulk mass and volume.

The program details reflect a consideration of the question, "What is

required?", "When is it needed?", "Will

large segments of the user community

benefit in any way?", "Will the technical competence of the section improve by

undertaking the task?", and "Are the necessary supporting services available?" With

regard to the latter question, this group

has been particularly successful in utilizing NBS resources outside of the group, and

other facilities in efforts supporting the

various tasks.

4.5 The Future

The most striking characteristic of the

Mass, Volume and Density Measurement System

is its apparent stability. For hundreds of

years, it has evolved by a slow linear ex- trapolation, each change firmly based on past experience. This apparent stability

comes in part from inertia of all parties

involved; the scientists and educators, the

suppliers of equipment and the users, and

in part from the fact that the needs which were the genesis of a formalized system

have not changed in centuries. The impact

of near revolutionary changes over the past

25 years has influenced not only the entire

system, but the current role of NBS and

other national laboratories and will indeed

influence the future as well.

Considering the system as two elements,

one including activities associated with

the definition of the unit, and the other

including activities associated with the

dissemination of the unit, the future of

the former element is by far the easiest

to discuss.

With regard to the defining artifact, the

national laboratories collectively will re- solve the problems associated with the variability of the platinum-iridium alloy

53

kilograms and the transfer of the mass unit

as embodied in these artifacts to artifacts

made of other materials such as stainless

steel, or single crystal silicon. The

technology is available and it is only a matter of concentration of effort. While

NBS will have a role in this work, relative

to practical mass measurement, these problems are largely academic, the resolution

of which will be beneficial to a relatively

small segment of the scientific community.

Undoubtedly, isolated efforts will be made

to construct a mass unit based on a con- stant of nature. Should these efforts be

successful, the results will be limited by

the complexity of the measurement technique

to definition of the unit and is not likely

to be competitive with the artifact-based

system for some time.

With regard to dissemination, the

current practices originated at the turn

of the century. Today, there is no technical reason why BIPM cannot be given the

responsibility for the transfer of the mass unit from the defining artifact, whatever it may be, to practical artifacts

for all who have need for direct access to the unit. In fact, such is being recom- mended informally to emerging nations by

both BIPM and others who are knowledgeable

concerning mass measurement. A decision

to centralize first level dissemination

of the unit would be advantageous from

both an economic and a scientific point of

view. It would, however, effect the current roles of some of the various national

1 aboratori es. One factor which will set the level of

the routine access to the unit as currently provided by NBS is dependent upon the

degree to which those who provide goods

and services are required by law or regulation, to defend their measurement

practices or results. Most of the current

requests for calibration in mass, volume

and density could be technically satisfied by referral to others, e.g. state

laboratories, manufacturers, commercial

laboratories, or by the users themselves.

Such facilities, however, do not generally have sufficient stature to alleviate

questions which could arise in a defense

situation, e.g. questions concerning

adequacy of method and results, questions

concerning "unbiased" results, questions

concerning the adequacy of alternate

methods and procedures relative to those

which are specified in contracts or regulations. The prudent entrepreneur is now reluctant to utilize services other

than those of NBS and if increased pressure is placed on measurement defense,

will be more so. Increased pressure on
the defense of measurement results will

bring an increased calibration load, or

will require a mechanism to extend the

present NBS "disinterested third party

blanket" to cover other facilities.

In terms of the immediate future, NBS

must continue to maintain and provide

access to a practical mass scale of sufficient quality to serve all of the needs

of the country. The mechanisms for such access, however, are influenced by both

the quality of the instrumentation generally available to the user and the level of

adequacy required for his particular task.

Transfer of the unit to certain equipment

manufacturers with minimum degradation

will be a continuing need. With regard

to the general user, however, the quality

of the instruments has reached the point

where sophisticated time-consuming efforts

are necessary to characterize their performance. Simple procedures to verify adequate performance relative to end use requirements will not require traditional access to the mass scale. This in turn

will further erode the calibration work

load.

There are requirements for mass, volume

and density measurement instrumentation

(or systems) which are beyond the capabilities of commercially available equipment. For economic reasons, commercial

equipment features rapid, convenient measurement at a precision level adequate for

the largest majority of users. It is not

practical for most manufacturers to consider modifications to production

units to improve performance beyond an order of magnitude or to undertake the

development of precise instruments for a limited market. An increasing role of NBS

in areas where the requirements are beyond

the capabilities of commercial equipment

is consultation relative to increasing the

precision of measurement and, in situations

where the need is relative to the health

and welfare of the nation, the development

of adequate prototype measurement systems.

For such services to be effective, however,

requires that "hands on" measurement

activities, e.g. the providing of routine

calibration, must remain above some

"critical level," even if artificially

generated.

5. SUMMARY AND CONCLUSION

cannot be resolved by NBS, e.g. social

implications of change and a large scale

education program relative to the fundamentals of measurement. While NBS is a partner in the literally millions of mea- surements which are made each day, by

providing access directly or indirectly

to the unit as requested and by acting as an unbiased reference in the case of

dispute, it is presumptuous to assume

NBS to have much, if any, real leverage

relative to the activities of the system.

Over the course of history the development of commerce and industry has been

first the recognition of need and then

the application of ingenuity to satisfy

that need. This has not changed in principle, only in complexity. Scientific data

and measurement fundamentals are partners

in such a system, while standards serve only to smooth the interactions between

various elements of the system. Very

few tasks require the ultimate measurement capabilities, e.g., studies of

fundamental constants and certain

classified requirements. For the

remainder, there are numerous solutions

which will produce adequate results, the

final form of which depends on many

factors.

In one sense, NBS has utilized its basic

assets (motivation, resources and time) to

develop a competence in determining realistic requirements and in provided guidance

in the development of processes which will

meet such requirements in the most economical manner. There are, however, economicpolitical -social forces, both with NBS and

within the system, which strive for a more

tightly governmental ly controlled system

resulting in new responsibilities for NBS

which may or may not be within the present

capabilities of the organization. In the

absence of major change, as might be imposed on the structure by these forces,

the current level of effort at NBS is con- sidered sufficient to maintain a minimal

level of competence, to maintain an adequate access to the unit, to maintain

reasonable progress in the advancement of

measurement application and capability.

Decreases in staff size or level of support

would result in essentially zero progress

in one or more of these areas.

The national measurement system for

mass, volume and density is stable and adequate relative to the needs as currently

perceived. There are some questions con- cerning the efficiency of the current mea- surement efforts within the system which

54
REh ERENCES

[1] Childe, Gordon, V., The Prehistory of

Science: Archaeological Documents, Part

1, The Evolution of Science, Readings

from the History of Mankind, edited by

Metraux, Guy S. and Crouzet, Francois,

pp. 72-75 (New American Library (Mentor

Books), New York, 1963).

[2] Cajori, Florian, Translation and

explanatory appendix, Sir Isaac Newton's

Mathematical Principles of Natural Philosophy and His System of the World, pp. 38-639 (University of California Press,

Berkeley, 1947).

[3] Rutherford, D. E., Classical Mechanics,

Ch. 2, ( Interscience Publishers, Inc., New York, 1951 ).

[4J Potius, P. E., Mass and Mass Values,

Nat. Bur. Stand. (U.S.), Monogr. 133,

p. 12, (1974).

[5] Tittman, 0. H, The National Prototypes

of the Standard Metre and Kilogramme;

U.S. Coast and Geodetic Survey, Appendix

No. 18—Report for 1890.

[6] Cook, A. H. and Stone, N. W. §., Precise

Measurements of Mercury at 20 C- I, Phil. Trans. Roy. Soc. 250A (1957).

[7] Cook, A. H., Precise Measurement of the

Density of Mercury at 20 C- II, Phil.

Trans. Roy. Soc. 254 (1061-2).

[8] Bowman, H. A., Schoonover, R. M. , and

Carroll, C. L., A Density Scale Based

on Solid Objects, J. Res. Nat. Bur. Stand. (U.S.), 78A (Phys, and Chem. )

,

No. 1 pp 13-40 (Jan. -Feb. 1974).

[9] API Standard 2550 "Calibration of

Upright Cylindrical Tanks", Amer. Pet.

Inst. 2101 L Street, N.W., Washington,

D.C.

[10] Page, C. H. and Vigoureux, P., The In- ternational System of Units (SI), Nat.

Bur. Stand. (U.S.), Spec. Publ. 330

(Apr. 1972).

[11] Pontius, P. E. Notes on the Fundamentals of Measurement and Measurement as

a Production Process, Nat. Bur. Stand.

NBSIR 74-545 (1974).

[12] Belew, L. F., Stuhlinger E., Skylab--A

Guidebook, National Aeronautics and

Space Administration (EP-107), pp. 161,

179, (1973).

[13] The International Bureau of Weights and

Measures, 1875-1975; NBS Special

Publication 420.

[14] Moreau, Henry, The Genesis of the Metric

System and the Work of the International

Bureau of Weights and Measures, J. Chem.

Educ. 30, p. 3 (Jan. 1953).

[15] Glazerbrook, . ., Dictionary of Applied

Physics, p. 777.

[16] The International System of Units (SI),

NBS Special Publication 330.

[17] Thiessen, M. , Schell, K . , Disselhorst, H.,

Wiss. Abh. Phys.-techn. Reichsanst 3,

1-70 (1900).

[18] Chappuis, P., Trav. mem. BIPM 13, DlD40 (1907).

[19] Tilton, L. W., Taylor, J. K. , J. Res. Nat. Bur. Stand. (U.S.) 18, 205 (1937) R.P.

971

.

[20] Guillaume, C. E., Trav. mem. BIPM 14,

A1-A276 (1910).

[21] Chappuis, P., Trav. mem. BIPM 14, BlB163 (1910).

[22] deLepinay, J. M., Buisson, H., Benoit, J.R.,

Trav. mem. BIPM 14, CI -CI 27 (1910).

0 [23] Friedman, I., Redfield, A. C, Schoen, B.,

Harris, J., Rev. Geo. 2, 177-224 (1964).

[24] Redfield, A. C, private communication

(H.A. Bowman).

[25] Woh, M. and Urey, H. C, J. Chem. Phys.,

3, 411-414 (1935).

[26] Christiansen, Crabtree, Loby, Nature

135, 870 (1935).

[27] Wagenbreth, H. and Blanke, W., Official

Journal of the Physikal ische-Technische

Bundesanstahlt, pp. 415-415 (June 1971).

[28] Bowman, H. A. and Schoonover, R. M., J. Res. Nat. Bur. Stand. (U.S.), 69C (Eng.

and Instr.), No. 3, pp. 217-223 (1965).

55
[29] Bowman, et al .

, see [8].

[30] Bowman, H. A. and Gallagher, W. H. , An Improved High Precision Calibration

Procedure for Reference Hydrometers,

J. Res. Nat. Bur. Stand. C, Engrg.

and Instr., Vol. 73C, July-Dec. 1969.

[31] Bulletin de L' Organization Internationale de Metrologie Legale, No. 56,

pp. 28-29 (Sept. 1974).

[32] Hartman, J., Dictionary of the United

States Standardization Activities, Nat. Bur. Stand. (U.S. ) Misc. Publ. 288

(1967).

[33] Cavanaugh, W. T., Measures of Success,

ASTM Standardization News, Vol. 2, No. 3, p. 27 (March 1974).

[34] Landvater, J., private communication,

Ohaus Scale Corp., Florham Park, NJ

.

[35] Johnson, A., Two Picrometers of

Increased Convenience and Precision,

J. Res. Nat. Bur. Stand. C, Engrg.

and Instr., Vol. 69C, No. 1, Jan.-

March 1965.

[36] Pontius, P. E., Measurement Philosophy

of the Pilot Program for Mass Calibration, NBS Tech. Note 288, May 6, 1966.

[37] Corwin, A. H., Weighing: Chapter III Techniques of Organic Chemistry,

Vol. I, Part I (Physical Methods of

Organic Chemistry), Interscience

Publishers, Inc., New York, 1959.

[38] Macurdy, L. B., Measurement of Mass,

Treatise on Analytical Chemistry,

Edited by Kolthoff, Elving and

Sandell, Part I, Vol. 7, Interscience Publishers, New York, 1967.

[39] Smithsonian Physical Tables, Smithsonian Miscellaneous Collections,

Volume 120, The Smithsonian Institution, Washington, DC, 1954.

[40] Pontius, P. E., Mass Measurement: A Study of Anomalies, Science, Vol. 190,

pp. 379-380, 24 Oct. 1975.

[41] Menache, M. and Girard, G., Concerning

the Different Tables of the Thermal Expansion of Water Betweem 0° and 40°C,

published jointly by the Institute

Oceanographique and the B.I. P.M. (1972).

[42] Emmet, R.T. and Miller, F.J., The

Density of Oceanograph Standards, in

preparation (1973).

[43] Bowman, H.A., Schoonover, R.M.,

Cartesian Diver as a Density Comparator, J. Res. Nat. Bur. Stand. C,

Engrg. and Instr., July-Sept. 1965.

[44] Private communication, G. Girard,

BIPM, Sevres, France.

56
APPENDIX A. METHODOLOGY OF THE STUDY

The material in this study was based on a number of published and unpublished documents. Extensive use was made of the files

of the NIBS Mass and Volume Section. Material

on the program of the NBS Office of Weights

and Measures and its relations with the

National Conference on Weights and Measures

was obtained from the annual reports of the

latter body. Additional information was obtained from the staff of the NBS Office

of Weights and Measures. With respect to the International Organizations, use was

made of material prepared for the U.S.

Advisory Committee on the International

Organization for Legal Metrology by the NBS

Engineering and Products Standards Division.

Data on NBS customers was developed from the

files of the Office of Measurement Services.

A survey was run of selected customers,

using economic data from Standard and Poor's

Index of Corporations, Dunn & Bradstreet,

and Moody's Handbook of Common Stocks. For

the purposes of our study, we have sought to

obtain trends in the interpretation of our customers' Standard Industrial Classification codes instead of attaching significant

weight to the individual numbers since many

of our customers are conglomerates.

A canvass of industry was made to establish a preliminary data base to confirm a few of our basic ideas concerning the structure of the mass measurement systems. The canvass consisted of two parts: an informal

question letter and/or telephone interview

with responsible individuals within an or- ganization. In all cases no formal questionnaire was sent "blindly" into an organization. A high-ranking contact within a company was first established within our

area of interest; a preliminary telephone

interview was conducted; and if the need

existed, a letter outlining other detailed

questions was subsequently sent to the interviewee for his comments. An effort was made to look objectively at our NBS Customer

Profile and select the SIC categories which

could be interpreted to imply "first-order

measurement-intensive" industries. By

selecting companies from our customer list

which possessed the majority of these codes

within their products or services rendered, we were able to develop a systematic

"sample" of the users. The canvass questionnaire is reproduced below:

PLEASE COMMENT ON AS MANY QUESTIONS AS POSSIBLE. USE ADDITIONAL SHEETS OF PAPER TO

PRESENT YOUR VIEWS. ALL ANSWERS WILL BE STRICTLY CONFIDENTIAL. COMPLETION ON OR BEFORE NOVEMBER 5 WOULD BE APPRECIATED.

1. EXPLAIN THE NATURE OF YOUR BUSINESS IN TERMS OF SERVICES AND PRODUCTS RENDERED.

PLEASE LIST AS MANY USES AS YOU ARE AWARE

OF FOR MASS DETERMINATIONS. BE SPECIFIC.

2. HOW MANY DOLLARS AND/OR MAN YEARS DOES

YOUR COMPANY EXPEND ANNUALLY IN SOME

FACET OF MASS MEASUREMENT? IS THERE SOME

COST-EFFECTIVE FIGURE THAT HAS BEEN COMPUTED IN TERMS OF THE INVESTMENT IN MASS

DETERMINATIONS VERSUS PRODUCTIVITY?

3. IF YOU ARE A BALANCE AND/OR WEIGHT MANUFACTURER, PLEASE GIVE THE NUMBER AND SALES OF BALANCES ANNUALLY AND ALSO THE NUMBER AND SALES OF WEIGHTS.

4. WHO ARE YOUR MAJOR CUSTOMERS AND THEIR

USERS (INTERNAL AND EXTERNAL) WITH

RESPECT TO MASS DETERMINATIONS? PLEASE

SPECIFY IN DETAIL THE ACCURACY AND PRECISION YOUR USERS NOW REQUIRE AT EACH

STEP IN THE TRANSFER. IS THERE A FORESEEABLE NEED FOR GREATER ACCURACY AND PRECISION? IN OTHER WORDS, ARE YOUR

CUSTOMERS REALLY USING ALL THE ACCURACY

YOU NOW SUPPLY THEM? IF NOT, WHY NOT?

(WE NEED AN EXHAUSTIVE ANSWER TO ALL OF

NO. 4).

5. WHAT TYPES OF INSTRUMENTATION FOR MASS

DETERMINATIONS ARE USED IN YOUR

FACILITY? HOW DO YOU PROCEED IN THE CALIBRATION OF THESE DEVICES?

6. TO WHAT EXTENT DO REGULATORY AGENCIES

(LOCAL, STATE, FEDERAL) GOVERN THE PRODUCTION AND/OR SALES OF BALANCES AND WEIGHTS?

7. DO YOU KNOW OF ANY PROBLEMS IN MANUFACTURING PROCESSES WHERE AN IMPROVEMENT

IN THE ACCURACY OR PRECISION OR METHOD

OF MASS MEASUREMENT MIGHT HELP RAISE

PRODUCTIVITY?

8. WHAT TYPE OF PERSONNEL DO YOU HAVE IN- VOLVED IN MASS MEASUREMENTS? IS THERE

ANY TYPE OF ADDITIONAL TRAINING YOU WOULD LIKE THESE PERSONNEL TO RECEIVE?

IN WHAT AREAS?

9. DO YOU FEEL THAT IF YOU HAD TO "PROVE"

THE ACCURACY OF YOUR MEASUREMENTS IN A COURT OF LAW, YOU WOULD HAVE SUFFICIENT

EVIDENCE TO CONVINCE THE JURY? WHAT

TYPE OF EVIDENCE WOULD YOU PRESENT FOR

YOUR DEFENSE?

10. IF YOU USED THE SERVICES OF NBS, PLEASE

STATE IN WHAT WAY. IF YOU ARE INVOLVED

IN THE MASS MEASUREMENT ASSURANCE PROGRAM (MMAP) PLEASE SPECIFY IN DETAIL
YOUR LIKES AND DISLIKES. HOW CAN ANY, OR

ALL, OF THESE SERVICES BE IMPROVED?

11. WHAT TYPE OF TRAINING SEMINARS AND/OR

PUBLICATIONS WOULD YOU LIKE TO SEE EMANATE FROM NBS? IN WHAT AREAS OF INTER- EST? TOWARD WHAT LEVEL OF PERSONNEL

SHOULD THESE BE GEARED?

A typical response to the above questionnaire is this:

" 1. Our laboratory is under contract with

the Atomic Energy Commission. Nature

of work is classified and relative to the National Weapons Defense Complex.

Mass determinations are used in:

1. Research and development of

explosive and nuclear items.

2. Mass Standards Laboratory - Calibration of weights and

balances.

3. Production of miniature detonators and associated

devices.

" 2. Seven man years are expended annually

for calibration and maintenance of

balances and weights. In addition,

an undetermined number of scientists,

technicians and workers use balances

in their daily work assignments.

" 3. Does not apply.

" 4. Users of mass measurement equipment

cover a wide spectrum as stated in

Question No. 1. Accuracy and precision required vary according to use and range from being able to use

a substitution balance without

where + .010 milligrams is required at

the first transfer level (weight

calibration)

.

" For example: Products being developed in

the R&D areas may require a + .OlOmg

uncertainty. Calibration of the mea- suring equipment requires a minimum

uncertainty in the mass standards, as the balance used in the areas consume

most of the allowable error. Miniature detonators require weighings

less than 50mg to an uncertainty of + .2mg. Check standards used with

this production equipment must be held

to less than + .015mg if product is to

be within the accepted tolerance.

" Accuracy and precision requirements in the

Mass Standards Laboratory are adequate, but can be reduced further if

applying corrections to micro work

necessary. Production requirements are constantly changing and are generally

more difficult to meet each year.

Improvements are needed in weighing

equipment available from the manufacturer and not from the laboratory or NBS calibrating organization. In most

cases, the customer is using the

accuracy supplied.

" 5. Our laboratory has over 600 mass mea- suring instruments, representing most

manufacturers, ranging from platform

scales to quartz fibre microbalances.

Most instruments are commercially

acquired, although some balances are customized or adapted to our particular needs. Majority of equipment is

substitution type analytical balances.

Others include:

Torsion Type Prescription

Top Loaders

Two Pan Free Swinging

Two Pan Electronic

Torsion Roller Smith Type

Quartz Fibre

" Procedures for calibrating vary according

to balance design and intended use. Internal weights are calibrated for

bias. Precision is determined by

repeated weighings at designated

loads.

" Standard balances are calibrated via the

National Bureau of Standards Mass

Measurement Assurance Program.

" 6. Local, State or Federal agencies do

not govern the production and/or sales

of balances and weights. There is no noticeable effect on weighing equipment from these agencies.

" 7. None

" 8. Personnel involved in mass measurements are hired as unskilled and

untrained. Our Mass Standards Laboratory provides a training class to provide the necessary training to

operate the equipment proficiently.

No additional training is required.

" 9. Sufficient evidence is maintained to prove the stated uncertainties in our Standards Laboratory mass measurement

process. Statistical data and control

charts furnished by the National

Bureau of Standards Mass Measurement

Assurance Program are maintained for

this purpose. Similar information is

58
available for production balances when

weighing to tolerance approaches the

capability of the equipment used.

"10. Our laboratory is an active participant in the National Bureau of Standard's Mass Measurement Assurance

Program. There is very little criticism of the program; the calibration

data received has been extremely beneficial to our organization and the

assistance and cooperation from NBS

personnel is above our expectations.

The turn-around time on some jobs is

less than desirable at times, and more frequent issue of up-to-date

control charts would be advantageous.

"11. I would personally like to see more

detailed procedures written in

"users'" language on calibration procedures relative to mass measurements,

other than weight calibrations. For

example, procedures for calibrating

small glass volumes and density measurements. Bowman and Schoonover's

paper "Procedure for High Precision

Determinations by Hydrostatic Weighing" is an excellent document, but

unsuitable for routine density measurements. A less complicated proven

procedure is desirable in many

laboratories.

Mr. David M. Jeffers

Administrative Technologist

Department of Pathology

York Hospital

York, Pennsylvania 17405

Mr. Robert Schoeneman

Internal Revenue Service

Alcohol, Tobacco and Firearms Division

Washington, D.C. 20226

Mr. Charles Muirhead

National Ocean Survey

Oceanographic Division

6001 Executive Blvd.

Rock vi lie, Maryland 20852

Dr. James D. MacLowry

Clinical Pathology Department

Clinical Center

National Institutes of Health

Bethesda, Maryland 20014

We have not limited our contacts to the

industrial community; indeed, we have established contacts within other governmental

agencies, hospital and laboratory personnel,

and also medical societies. Specific

contacts include:

Mr. Charles Stockman

Maryland Office of Weights and Measures

Department of Agriculture

College Park, Maryland

Mrs. Martha Winstead

Quality Control Coordinator

Southbend Medical Foundation

Southbend, Indiana

(219)234-4176

American Society for Medical Technology

Ste. 200

5555 West Loop South

Houston, Texas 77401

(713) 664-8121

59
APPENDIX B

The past of the Mass and Volume Section

is inseparably intertwined with the history

of Weights and Measures and NBS. As one re- views this history to identify strengths and

weaknesses, one cannot help but note the

progress of people through the organization

over the years. As people move through the

organization, so move philosophies and the

way things are done, and to some extent, the

way others view NBS. One can see, through

the anecdotes of the past, only a generation

removed, and through reviews of the historical records, a pattern which not only re- flects the development of the section, but

also of the NBS as a whole. Historically,

it doesn't really matter why certain things were done; it is certain that the reasons appeared to be valid to those faced with the

decisions which had to be made, but what was

done is important to an understanding of why

things are the way they are today. For the

purpose of this discussion, the history of

the section, and NBS, has been arbitrarily

divided into "eras," which, in addition,

have been arbitrarily named "Getting

Started," "Confusion," "Transition," and "A New Start.

"Getting Started"

The basic tools of the trade are not new, the balance originating some time in the

Bronze Age, and with "traceabi 1 i ty " of the

unit over at least 4500 years going back to Nebuchadnezzar. The mathematical tools also

originated far back in time, with averaging

in the days of the Romans . Weighing by substitution, normally called "by the method of

Borda," was used by Amiot in 1776. Transposition weighing, "the method of Gauss," and

"least squares," are attributed to Gauss in

the early 1800' s. It is doubtful, however,

that Gauss invented transposition weighing

since it is the basic method of testing an equal -arm balance. He may, however, have been

the first to treat the method in a mathematical analysis. Weighing designs started with

Tartaglia in 1556, and Bachet in 1612, with

later contributions by Hassler in 1817 and

Broch in 1886. The science (or art) of mass

1 This, and the balance of this paragraph is an extremely brief summary of the history

presented by C. Eisenhart in references

[1] and [2].

60

measurement started in this country with

Hassl er. Hassler was a competent metrologist, com- parable with the builders of the kilogram in

France, and the reconstructors of the pound

in England. Fischer brought to the newly

formed NBS the disciplines of Hassler, as he

had learned them from those who had been instructed by Hassler himself [3]. He brought

with him the weighing designs of Hayford which

predate those of Benoit of BIPM [4,5].

Hayford's work has never been given the at- tention it deserves, perhaps because of the

prestigious position of Benoit, and the fact

that Benoit' s presentation was somewhat more

general. Fischer, together with his knowledge

and the standards from the Coast Survey, be- came a part of the Weights and Measures "Section" of Division 1, under the direct supervision of Stratton.

Among the earliest circulars of announce- ments of the services that the new NBS could

provide were those in the area of mass mea- surement and in the testing of glass volumetric apparatus. By 1910, Fischer was Chief

of the Weights and Measures Division, with

3 sections which were the genesis of the

present Mass and Volume Section, and 2 sec- tions which would eventually become the Office of Weights and Measures. Pienkowsky

was the Chief of the Mass Section through

1940. Circular 3, Design and Test of Standards of Mass, (Rev. 3), prepared by Fischer

and Pienkowsky, is a classic in the area of mass measurement.

Circular 3 treated both the problem of

design and adjustment of weights, and the

scientific use of mass measurements. For

commercial use, three sets of adjustment

tolerances were established: Class A, for

state standards; Class B, an intermediate

class which saw little use; and Class C, for

commercial weights. This tolerance structure evolved from an end use requirement,

that of weighing large quantities of materials with multiple lever scales. The problem was to establish a commercial tolerance

for "tip" weights which, when multiplied by

the lever ratio of the available scales,

The first five circulars are: NBS Circular 1 The National Bureau of

Standards

2 Measurements of Length and

Area Including Thermal Expansion

3 Design and Test of Mass

Standards

4 Verification of Standards of

Capaci ty

5 Test of Clinical Thermometers
would not introduce an unreasonable systematic error in the weight of the goods. Having arrived at these limits, Class B and

Class A tolerance limits were established

such that compliance with Class C tolerances

could be established with a minimum of mea- surement effort.

A story relating to the accomplishment of

the above task has been passed down from

those who were present at the time. Fischer

was in the habit of keeping notes on his

shirt cuff. The task of establishing the

tolerance structure had been under discussion for some time, and at such a noontime

discussion, Fischer worked out the toler- ances on his shirt cuff. He had them typed

immediately, but neglected to record the

logic behind their origin. The shirt was laundered and the detailed logic upon which

the structure was based was gone forever.

Pienkowsky was a tough taskmaster. Two

types of calibrations were offered, one re- sulting in a "test report," and the other in

a "certificate." The issuance of a "test report" usually meant that something was inferior, that the item did not warrant the

best effort. Years of experience were re- quired before one was qualified to work with

items which warranted a "certificate."

Weighing designs were used in both cases,

and the quality of the measurement was es- tablished by the use of "check equations,"

e.g., if A-B=X

1 , B-C=Xp and A-C=X3

, then, if

all is in order (X1+X2T-X3, the "check equation" should be within some established limit.

While Pienkowsky was the only one who knew the

basis for the established limits, everyone in

the group knew what they were and strived

mightily to have their work be acceptable.

In this era the thermal problems of the

equal arm balance were not as yet understood. The best work was done in isolation.

Computations were done by hand with the use

of slide rules and logarithmic tables. The

work was checked and rechecked. Work on large capacity scales, and the testing of

railway track scales started in about the

middle of the "era." A large effort was devoted to the testing of all kinds of large

scales in addition to the railway track

scales. With the track scale test cars operating out of a field station on the outskirts of Chicago, a truck equipped with

large weights and weight handling equipment

1 Each operator was assigned a specific

colored pencil, thus from the array of

colored check marks on the computation

sheet, one could identify the various

"checkers.

operated out of Washington. For remote

scales, such as mine tipple scales, a large

number of commercial 50 lb weights had to be

"manhandled" to the scale location. With

practice, one could pick up two in each

hand, an amazing feat which no doubt supplemented the paycheck through side bets with

the miners.

With the organization of the National

Conference of Weights and Measures in 1912,

additional sections were added to the Metrology Division to support that organization. This action initiated a rift which,

up to now, is only partially repaired. Pienkowsky, in charge of mass measurements,

was concerned with the scientific aspects of mass measurement up to 50 pounds, yet had to interface with both the Scale Unit and the

legal aspects of weighing. The Scale Unit,

because of the handling difficulties with

large weights, was primarily engineering,

and, to some extent, art oriented. The

Scale Unit was concerned with the correctness of the result relative to a particular

usage. The Weights and Measures Unit was concerned primarily with the legal aspects

of metrology, e.g., right by definition.

The Mass Unit insisted that the balance was

a mass measurement device. The Scale Unit

was more oriented in the practical usage of

large weights; the Weights and Measures Unit

was only interested in establishing systems

which could not be attacked legally. Two

anecdotes clearly illustrate the rift.

While the Weights and Measures Unit was stressing the importance of standards, one member of the Scale Unit would on occasion,

and much to the dismay of the Weights and

Measures Unit, calibrate a standard with a collection of flat irons, frying pans, stove

lids and the like, all of which had been

carefully calibrated in advance. State

weights and measures people were taught to

(1) pick up the weight in both hands (so as not to drop it), (2) approach the balance

with care (so as not to fall), (3) bow

slightly (so as to clearly identify the

weight before it was placed on the balance

pan), (4) place the weight gently on the

balance pan, and do likewise for the second

weight. Without the reasons which, of course, were a matter of routine within the

Mass and Scale units this was interpreted as

(1) approach the balance with awe, (2) genuflect, (3) put the weight on the pan, and do

it all over again. Needless to say, there were very strong feelings between the various

sections.

The close of the "era" was largely a matter of coasting on reputation, or position.

Much time was devoted to detail of compliance with specifications, and to the extension of the tolerance limits to the variety

61
of weights in common use and some of which were not so common, the onza and adarme.

The program was in essence a semi regul atory action e.g., differentiating what would receive a "test report"

and what would receive a "certificate" increased. Aside from Circular 3, little was done to advance the understanding of mass measurement, and to provide a direct service

to the user. The Director signed each re- port, which in turn was embossed with the

official Bureau seal. Since weights could

not be "marked" without destroying the calibration, the "mark" was engraved on the case, which in turn was wrapped, tied with

red ribbon and "sealed" with sealing wax and

an appropriate signet.

" Confusion"

Reorganization early in the "era" changed

the Weights and Measures Division to the Me- trology Division and established the Office

of Weights and Measures under the direct

supervision of the Director. This action es- sentially severed the Office of Weights and

Measures from the support of the technical

divisions, including editorial review.

Authority to sign "Test Reports" and "Certificates" was delegated to the section. The

ritualistic procedures were, however, maintained.

About midway in the "era," the Mass Section and the Scale Section were combined and

transferred to the Mechanics Division. This

placed the new section in the area of applied science. Circular 547, the first of a planned series, updated the design and tol- erance structure established in Circular 3. The philosophy of Circular 547 was oriented

more toward "what they should have" rather

than toward "what do they need." Manufacturers of weights were consulted and the

tolerance structure was based on their es- timates of the ability to adjust weights.

These estimates turned out to be optimistic

and, as a result, there were many rejections

for "out of tolerance." The situation was eventually resolved by revising the specifications.

This presentation e.g. is another example

of numerous attempts of NBS personnel to achieve a semi regul atory action, first the

preparation of the specification, then the

rejection for noncompliance. Much work was

1 The onza is the ounce of Spain and Spanish

America. The adarme is 1/16 of an ounce.

done on the drafts of the documents to follow 547, but none were completed and

pub! i shed.

Simplified procedures were published in

the area of volume and density measurements.

A method for testing the new quick weighing

balance was published. Under the urging of

the Office of Weights and Measures, a 1000

lb equal arm balance was developed [6].

By and large other publications of the "era" followed a rather fixed pattern: general

classes of equipment were described together

with brief outlines of test procedures used

by NBS; some form of tolerance structure was presented; detailed discussion of what was

necessary to receive a "certificate," and

what would get only a "test report;" and

finally a description of the mechanism

whereby one submitted items to NBS for test. Toward the end of the "era," the Mass and

Scale Section was once again returned to the

Metrology Division. At approximately the same time, the Office of Basic Instrumentation was established under the supervision

of the Director and the position of Assistant

Director for Testing was established.

With regard to the section, in spite of internal conflicts between the Mass Unit and

the Scale Unit, this marked the start of

real progress, particularly with respect to the studies of the balance. The influence

of the Statistical Engineering Laboratory,

established in the late 1940's was beginning

to be evident in the calibration programs.

Higher management decisions, however, en- couraged dissemination through equipment

manufactures and networks of calibration

laboratories. The success of such an action

presumes that the second level laboratories

assume the role of interfacing with the user. As it turned out, the second level

laboratories elected to become "carbon copies" of NBS. Somewhere along the line, a "hierarchy" became firmly entrenched, with

mission oriented facilities located several

steps removed from NBS, and with no direct

communication.

With respect to manufacturers, with tacit

NBS approval, calibration "certificates" and

the like were a part of doing business with

the "hierarchy," with NBS frequently being a de facto extension of the manufacturer's

quality control organization. It was a com- mon practice for manufacturers and distributors to stock NBS calibrated items, with an add on "handling" charge far in excess of

the NBS fee for the work. The practice of

doing calibration work for manufacturers and

distributors was encouraged by the use of

"number of items calibrated" as a measure of

the effectiveness of the section.

By the end of the "era," several basic

papers had been published with regard to de62
tailed studies of balance characteristics

[7, 8, 9, 10, 11]. The development of a precision kilogram balance had been started.

Methods for calibrating weights in the

direct reading balances were developed and

published. The two-knife constant load 50

lb balance was at the state of evaluation of

the development model [12]. The program for

new state standards had been prepared. The

"era" closed with the introduction of "trace- ability" through U. S. Air Force Bulletin No. 520. The introduction of the concept without

definition created an endless scene of confusion.

" Transition"

The "transition" era included both the

change from the monolithic structure of NBS

to the present Institute structure, and the move from Washington to Gai thersburg. Hallmarks of the era were the technological ex- plosion of the space age and the start of

an extensive re-evaluation of the role of

NBS. The "up through the ranks" method of

filling vacancies was wanning, with new faces

and new ideas appearing at all levels of

management. The National Conference of

Standards Laboratories was formed, thus uniting those who were faced with carrying out

the quality control aspects of government

procurement in the area of space exploration

and defense. MIL-C-45662A, Calibration

System Requirements, provided in part the

missing definition of "traceabi 1 i ty.

Eisenhart's classic paper, "Realistic Evaluation of Precision and Accuracy," was presented in 1962 [13]. In 1963, by decree,

uncertainty statements were required on all

reports. Later that same year "certificates" were abolished, a positive move

away from the semi regul atory action associated with the previous "report" and "certificate." Measurement results were reported

on a "Report of Calibration." Where a "certificate" was mandatory, the institute

Director would "certify" only that the

measurements were made.

Early in the "era" there was a growing

divergence of opinion concerning the interfacing of NBS with the users of the calibration services. At the section level, it was recognized that various end use requirements

could not afford the degradation of the

units through a hierarchy of calibration

laboratories, and that there was a real need

for the dissemination of measurement procedures. Most echelon laboratories were more concerned with emulating NBS than with

being centers of measurement excellence.

Lower level laboratories were faced with

real measurement problems. The Assistant

Director for Testing, however, was slow in

recognizing this need, with the result that

frequently NBS was presenting two "faces" to the users. With the press of cost-effectiveness measures, by the end of the era it was recognized in part within NCSL that the

role of the calibration laboratory was

1 imi ted.

Through this era, the Mass and Volume

Section completely revamped both the program

structure of the section, and the services

provided. Each action, starting with obtaining a commitment from the Statistical

Engineering Laboratory to support the evaluation of the measurement processes, was the

result of micro-issue and micro-measurement

system studies completed prior to starting

the action. The capabilities of the section were augmented with the increasing use of

computers, both time sharing and otherwise.

The section staff, relieved from the tedious

detail of checking and rechecking, could

finally begin to think about what they were

really doing.

The first computer prepared report substantiating a measurement process operating

in a state of statistical control was issued

in late 1963. A large educational effort

in mass measurement techniques, and in the

characterization of measurement processes, was a part of the work with weights for

force machines. Studies were made concerning the performance characteristics of mass measurement processes in other facilities.

In late 1965, the Director of IBS gave verbal approval to proceed with the Mass Measurement Assurance Program (called at the

time the Pilot Program in Mass Measurement).

By late 1967, the program was operational,

and tests were underway to evaluate, for

the first time in a controlled manner, the

measurement capabilities of one segment of

the national measurement system, that asso- ciated with mass measurement.

Throughout this era there was a steady

flow of papers, both tutorial and technical.

Training conferences were held at NBS, and

the section staff was invited to describe

the programs at various meetings of professional societies. By virtue of a knowledge

of the measurement process parameters, the

"lost time" on the move to Gai thersburg was

less than one week. One particularly difficult task associated with the move con- cerned the facilities which had been designed

1 With the introduction of computer prepared

reports, many of the rituals, including

tying packages with red ribbon, sealing

with wax and an official seal, were

di scarded.

63
and constructed on the basis of the

anticipated role of the sections in

the mid 1950' s and which, by now, had con- siderably changed.

" A New Start"

This is the current era, and from the

standpoint of calibration services, it is

the era of the Measurement Assurance Programs. In the early days of this era, the

Director of IBS established the Office of

Measurement Services as an operating Division, and for the first time, NBS was able

to present one "face" to the users of the

calibration services. Efforts to unify the

activities within the Metrology Division by

the establishment of branches were not suc- cessful. In early 1970, the Metrology Division was disbanded, and the activities were combined with those of the Atomic Physics

Division to form a new division, the Optical

Physics Division. Immediately following,

the Mass and Volume Section absorbed the

Length Section and the Engineering Metrology

Section, becoming the Mass, Length and Volume Section.

From the formulation of the new section

until mid 1971, the activities were largely

directed toward cleaning up a large backlog

in the engineering metrology area, and in

the establishment of the Measurement Assurance Program in the area of gage block measurements. In mid 1971, the Dimensional

Technology Section was formed, assuming res- ponsibility for both engineering metrology

and length measurements (with the exception

of tapes). The responsibility for the com- pletion of the MAP program in gage blocks,

however, remained as a responsibility of the

Chief of the Mass and Volume Section, acting

as a Special Assistant to the Division Chief

for Measurement Assurance Programs.

The marriage of one of the most conservative areas of NBS with one of the most highly specialized scientific areas was to be an experiment. It is perhaps too early to evaluate the merits of the action. From the

metrologist's viewpoint, it certainly provided a wealth of resources, however, a great effort had to be made in order to formulate the myriad of problems in such a manner that (1) the problem is of interest to the scientist, and (2) that the results from

the scientist can be utilized in a practical

sort of way. The measurement expertise of

the section has assisted in certain areas,

e.g., the redetermination of Avogadro's number, but, with few exceptions, there was no

real interest in metrology to the depth

necessary for assistance in problem

formulation and solution.

Early in the era, the section accepted

the task of the application of measurement

process analysis techniques to the problem

of reprocessing spent reactor fuel elements

[14, 15]. This initial work was supported

by other agency funding. A continuing

activity over the era has been in consultation with appropriate committees working on specifications and guidelines for both mass

and volume measurements in this field. The

first specifications are now in the balloting stage, eventually to become ANSI

standards for the industry [16, 17].

In early 1972, a precision kilogram balance, NBS-2, was shipped to BIPM [18]. As a part of the transfer, BIPM personnel spent

approximately 1 month at NBS learning about

our procedures, methods of data analysis,

and the concepts of characterizing the performance of a measurement process. Over the

past few years this balance has been used to evaluate the stability of Pt-Ir kilograms in

preparation for planned intercomparisons of

prototype kilograms [19]. In 1973, a new version of the report of mass calibration

was introduced, a laboratory notebook type

of report with a complete documentation of

the measurements, and the status of the mea- surement process at the time the measurements were made. Much interest in these procedures

has been shown by both Italy and Sweden.

In late 1974 the gage block measurement

processes were operating in a state of sta- tistical control, with new reporting procedures, and the development of detailed MAP procedures were under discussion. Bowman et

al had completed the determination of

pure single crystal silicon, the basis for a solid density standard. With the publication of procedures for the calibration of

volumetric glassware, all of the procedures

now in use at NBS are in the literature

[20].

These brief remarks indicate the history

of the section and the manner in which it

has been operated over the years. The isolation with respect to the Office of Weights

and Measures remains (primarily at the man- agement level since the key working technical staff of OWM are former members of the

Mass and Volume Section).

The important contributions, other than

the direct support to certain specific areas

of science and that obviously associated

with providing access to the mass unit, have

been in the contributions to the understanding of the mass measurement process, and in

the applications of measurement assurance

procedures. The problems facing the section

at this time are (1) those associated with

the activities of the 0IML, which are regulatory in nature and obviously in direct con- flict with the directions of the section
activity over the past 15 years; (2) the

problems associated with the anticipated

recal ibration of the prototype kilograms by

BIPM, scheduled tentatively to take place

within the next several years; and (3) the

extension of the mass unit to practical mass measurement scales.

The present environment of NBS reflects

several distinctly different philosophies.

Perhaps the largest group is the highly specialized who, after a cursory look at the

role of measurement, has decided that the

"way to go" is to organize, or legalize,

measurement. The concepts of "certified

standards," and "traceabi 1 i ty" are the "obvious solution to all measurement problems"

and with the problem taken care of in this manner, one can go back to the more interesting things. This philosophy was strongly

advocated by the top administration up to the middle of the "transition era," at about

which time it reached its peak. When carried to the extreme, such a policy becomes

self-serving, that is, having created the

organization, one exists to support that or- ganization. In the meantime, there is little,

if any, direct support to the user. The opposing philosophy, originating in

about the middle of the "transition era" concerns the adequacy of the measurements

which have to be made by the user. Measurement assurance is merely doing what has to be done in order to be sure that the mea- surement is adequate for the intended use. To support this, one must look for the problems, then provide the most economical

solutions. Of course there is a need for

good standards, Standard Reference Materials

and the like, but they are means to an end,

not the end itself. Success is measured by

the status of the measurement system itself,

and not by the number of "certified standards" provided by NBS. To carry out such a program requires a willingness to learn, and

a substantial commitment of time on the part

of both NBS and the user. Needless to say, such programs are strongly supported from that

segment of the user community which has real

measurement problem but not in a coordinated

way. It is unfortunate that coordinated opposition comes from those who see NBS ac- tivities as a simple means to meet contractual

requirements.

65
APPENDIX B REFERENCES

[1] C. Eisenhart, "Some Antecedents of Modern

Experiment Design", Invited address before the Section of Statistics, ThirtyThird Annual Meeting of the Virginia

Academy of Science, Madison College,

Harrisonburg, Virginia, May 13, 1955.

[2] C. Eisenhart, "The Background and

Evolution of the Method of Least Squares"

34th Session of the International Statistical Institute, Ottawa, Canada, 21-29

August 1963.

[3] S. W. Stratton, "The Bureau of Standards

and its Relation to the United States

Coast and Geodetic Survey", Centennial

Celebration of the United States Coast

and Geodetic Survey, pp 33-34, Government Printing Office, Washington 1916.

[4] J. F. Hayford, "On the Least Square Adjustment of Weighings", United States

Coast and Geodetic Survey, Report from

1892, Appendix No. 10, Government

Printing Office, Washington 1893.

[5] J. P. Benoit, "Standardization of Sets

of Weights", Annalos des Poids et

Measures, Vol. 13, 1907.

[6] H. H. Russell, "The National Bureau of

Standards 1000 lb Balance", Scale

Journal, pp 6-7 (Aug. 1955).

[7] H. E. Aimer, "Response of Microchemical

Balances to Changes in Relative Humidity, J. Res. Nat. Bur. Stand. (U.S.),

64C (Engr. and Instr.), No. 4, pp 281-

285 (1960).

[8] Bowman, H. A., and Macurdy, L. B., "A Photoelectric Follow-up and Recording

System and its Application to Remote

Observations of the Beam in HighPrecision Balances", J. Res. Nat. Bu. Stand. (U.S.) 63C (Engr. and Instr.),

No. 2, pp. 91-96 (1959).

[9] Bowman, H. A., and Macurdy, L. B., "Gimbal

Device to Minimize the Effects of OffCenter Loading on Balance Pans", J. Res.

Nat. Bu. Stand. (U.S.) 64C (Engr. and

Instr.), No. 4, pp 277-279 (1960).

[10] Bowman, H. A. , and Aimer, H. E., "Minimization of the Arrestment Error in OnePan, Two-Knife Balance System", J. Res.

Nat. Bu. Stand. (U.S.), 67C (Engr. and

Instr.), No. 3, pp 227-235 (1963).

[11] Macurdy, L. B. and Alrner, H. E., J. Res

Nat. Bur. Stand. (U.S.), 68C (Engr. and

Instr.), No. 3, pp. 135-140 (1964).

[12] Aimer, H. E . , Bowman, H. A., Jensen,

M. W., Macurdy, L. B., Peiser, H. S.,

and Wasko, B., "A Direct-Reading TwoKnife 50-1 b Balance of High Precision

Suitable for State Weight and Measures

Laboratories", J. Res. Mat. Bur. Stand.

(U.S.), 68C (Engr. and Instr.), No. 3, pp. 141-154 (1964).

[13] Eisenhart, C, "Realistic Evaluation of

the Precision and Accuracy of Instrument Calibration Systems, J. Res. Nat.

Bur. Stand. (U.S.), 67C (Engr. and In- str), No. 2, pp. 161-187 (1963).

[14] Pontius, P. E., "Metrology of Nuclear

Materials", Nat. Bur. Stand. (U.S.) Report 9994 (Feb. 1969).

[15] Pontius, P. E., "On the Calibration of

Large Tanks", Nat. Bur. Stand. (U.S.)

Report 9993 (Feb. 1969).

[16] American National Standard N15.18, Mass

Calibration Techniques for Nuclear

Materials Control.

[17] American National Standard N15.19, Volume Calibration Techniques for Nuclear

Materials Control.

[18] Aimer, H. E., "National Bureau of Standards Kilogram Balance", NBS No. 2, J. Res. Nat. Bur. Stand. (U.S.), 76C (Engr

and Instr.), pp. 1-10 (1972).

[19] Girard, Georges, Private Communication,

BIPM.

[20] Lembeck, J., "The Calibration of Small

Volumetric Laboratory Glassware, Nat.

Bur. Stand. (U.S.), NBSIR 74-467 (1974)

66
NBS-114A rev. n-77)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 74-928

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE The National Measurement System for Mass, Volume and Density

5. Publication Date

M-.., | Q~7Q

6. Performing Organization Code

Paul E. Pontius, James R. Whetstone, and John A. Simpson

S. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. T70fl i r\r\

11. Contract .'Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP) 13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) This document, one of several similar documents resulting from the NBS study of

the National Measurement System, reflects the results of intensive studies

carried out from 1972-1975 relative to Mass, Volume and Density measurements

in the United States. The history and the current status of these measurements

is discussed as well as the relative role of NBS. A bibliography is included.

17. KEY TORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Density measurements; mass measurements; national measurement system; volume

measurements

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