Inside this Issue

Page

The Proper Use of Substitute Test 

Fluids 1

This Month in History 1

Calendar 2

Announcing the 96th Annual 

Meeting 5

Now Available, The NCWM 95th

Annual Meeting Report, SP 1115 6

Now Available the NEW Handbook

133, Checking the Net Contents of

Packaged Goods for 2011 6

This Month in 

History

June 5, 1968 - Robert F. Kennedy was assassinated after winning the California Presidential

Primary. He also served as the U.S. Attorney

General (1961 - 1964) during his brother John

F. Kennedy’s presidency.

June 6, 1872 - Susan B. Anthony, a pioneering

feminist, was fined for voting in a presidential

election in Rochester, New York. She worked

to extend the “right to vote” to females. This

privilege was not granted to women until August 1920 with the 19th Amendment to 

the U.S. Constitution.

June 6, 1944 - D-Day (WWII), Allied forces

landed in Normandy with the largest 

amphibious landing in history.

more history on page 4

1

Volume 2 Issue 3

June 15, 2011

The Proper Use of Substitute

Test Fluids

By Marc Buttler

Liquid-measuring devices are used in many different commercial applications. The vast array of liquid products that are measured includes some

products that may pose difficulties in testing. NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and

Measuring Devices, allows for substitution of fluids during testing in place

of the actual fluids that will be used in commerce to mitigate some of

these issues.

The most important consideration that will determine if one fluid can be

used as a viable substitute for another is whether the results of the testing with the alternative fluid will accurately predict the performance of

the device when measuring the fluid with which the device will normally

be used. This article provides some guidance and considerations to help

those who need to make decisions about whether or not to allow substitute fluids for testing.

HANDBOOK 44 NOTES ON TEST LIQUIDS

Within Section 3.30. “Liquid-Measuring Devices” of NIST Handbook 44,

paragraph N.1. “Test Liquid” makes the following statement: “The liquid

used for testing of a liquid-measuring device shall be the type the device is

used to measure, or another liquid with the same general physical characteristics.” The Handbook also states that “Following the completion of a

successful examination of a wholesale device, the weights and measures

official should attach a label or tag indicating the type of liquid used during the test.”

Similar statements also appear in other sections of the Handbook. For

example, Section 3.31. “Vehicle-Tank Meters” and Section 3.3. “Milk Meters” include the above statements and both of these Sections further

specify that, “A milk-measuring system shall be tested with the type of

milk to be measured when the accuracy of the system is affected by the

characteristics of the milk (e.g., positive displacement meters).” The latter example holds the key to understanding the phrase “another liquid

with the same general physical characteristics.” The intent of this statement is to allow a fluid to be used as a valid substitute for another fluid

during testing, so long as it is reasonable to expect that whatever differences do exist between the physical characteristics (properties) of the fluids will not have a significant impact on the meter’s performance and the

conclusions from the testing.
Calendar 2011

June 29

Verifying Proper Design of AZT (Webinar)

Contact: Rick Harhman at

richard.harshman@nist.gov

June 30

Proficiency Testing & Root Cause Analysis

(Webinar)

Contact: Val Miller at val.miller@nist.gov

July 7

Calibration Method Validation (Webinar)

Contact: Val Miller at val.miller@nist.gov

July 14

Basic Uncertainty Concepts (Webinar)

Contact: Val Miller at val.miller@nist.gov

July 17 - 21

NCWM Annual Meeting

Missoula, MT

Contact: info@ncwm.net

Website: http://www.ncwm.net

July 21

Documenting Traceability and Calibration Intervals (Webinar)

Contact: Val Miller at val.miller@nist.gov

July 28

Software Verification & Validation (Webinar)

Contact: Val Miller at val.miller@nist.gov

August 4

Internal Auditing (Webinar)

Contact: Val Miller at val.miller@nist.gov

August 11

Management Reviews (Webinar)

Contact: Val Miller at val.miller@nist.gov

August 21 - 25

NSCLI Annual Conference

Gaylord National Convention Center

National Harbor, MD

Contact: http://www.ncsli.org

August 31 - September 1

Weighing Sector Meeting

Sacramento, CA

Contact: info@ncwm.net

September 1

Calibration Report Evaluation (Webinar)

Contact: Val Miller at val.miller@nist.gov

continued on page 3

W&M Connection 2 Volume 2 Issue 3

JUSTIFICATIONS TO USE A SUBSTITUTE FLUID

Generally speaking, the most conclusive results can be obtained by testing

with the same fluid that is to be sold commercially (hereafter referred to

as the “primary fluid”). However, there are many reasons that may make

it impractical to use the primary fluid for testing. When there is good reason to justify the use of a substitute fluid for testing, the suitability of the

substitution fluid must be authorized by the regulatory official and must

also comply with any restrictions made by the meter manufacturer.

• In cases where handling of the product for the purpose of testing

may result in risks to safety, a substitute fluid may well be justified.

Testing methods often require greater exposure of the product to

people and the environment than is present during normal operation.

If testing with the primary fluid poses hazards, then a substitute fluid

that is safer for the testing should be considered if one is available.

• Certain products may also pose a risk of damage to the integrity of

the reference standards that are needed for a test. For example, a

product that might result in corrosion, erosion, or fouling of an otherwise carefully maintained and valuable field test standard would

clearly be something that the official would want to avoid.

• The cost and expense of testing will often be impacted by whether

the product used for test drafts can be returned to inventory for later

sale or must be discarded. It may be that the testing process renders

the product unsalable or that there is unacceptable risk of contamination due to the test. In such cases, substitution of an acceptable alternative fluid can help to avoid excessive costs that would be

prohibitive to a reasonable maintenance cycle interval.

Other reasons may arise to justify a substitute fluid and all should be considered on a case by case basis using good judgment to decide if they warrant the substitution of an alternate fluid. In any case in which a reason is

deemed to be justified, the need still remains to also confirm that the proposed substitute fluid complies with the statement that the fluid be “another liquid with the same general physical characteristics.”

SUBSTITUTE FLUIDS - THE FOUR KEY FACTORS

The suitability of a fluid for testing really depends on influence factors

that affect the measuring device that is to be tested. If a particular fluid

property (characteristic), such as density or viscosity, is known to have an

influence on the performance of the device to be tested, then it is important that any proposed substitute fluid have properties (characteristics)

similar to the primary fluid. Because different device technologies and

designs are affected by different influence factors, the type of measuring

device will determine the fluid characteristics that must be similar between the primary and the substitute fluids. For example, the performance of positive displacement meters is typically influenced by fluid

viscosity, whereas conductivity of a fluid may influence the performance

of a magnetic flow meter.

There are four key factors to consider while assessing the acceptability of

one fluid as a substitute for another:

• the DEVICE TYPE to be tested,

• the difference in the CRITICAL FLUID CHARACTERISTIC for that de-
September 8

Calibration Method Validation (Webinar)

Contact: Val Miller at val.miller@nist.gov

September 12 - 15

Central Weights & Measures Association

(Interim Meeting)

Cedar Rapids, IA

Contact: Vicky Dempsey at

dempseyv@mcohio.org

September 26 - 30 (Invitation Only)

OIML - TC 6 (Prepackaged Products)

NIST

Gaithersburg, MD

Contact: Kenneth Butcher at

Kenneth.Butcher@nist.gov

301-975-4004

September 26 - 29

Western Weights & Measures Association

San Luis Obisipo, CA

Contact: Brett Saum at bsaum@co.slo.ca.us

October 6

Annual Submission Process (Webinar)

(Limited to State Laboratory Participants)

Contact: Val Miller at val.miller@nist.gov

October 12 - 13

Northeastern Weights & Measures Association Interim Meeting

Norwich, CT

Contact: James Cassidy at

jcassidy@cambridgema.gov

October 13

Document Control & Recordkeeping (Webinar)

Contact: Val Miller at val.miller@nist.gov

October 21 - 22

NTETC Measuring Sector

Norfolk, VA

Contact: info@ncwm.net

October 23 - 26 

Southern Weights & Measures Association

Norfolk, VA

Contact: Dale Saunders at dale.saunders@vdacs.virginia.gov

November 10

Annual Submission Process (Webinar)

(Limited to State Laboratory Participants)

Contact: Val Miller at val.miller@nist.gov

continued on page 4

W&M Connection 3 Volume 2 Issue 3

vice,

• whether or not the two fluids are in the same PRODUCT CATEGORY

TEST REQUIREMENT GROUP for that device, and

• the difference in OTHER FLUID CHARACTERISTICS IDENTIFIED BY

THE MANUFACTURER as important for that device.

Device Type. The reason that the type of device is such an important

consideration is that some fluid characteristics affect different device

types differently than they will other device types. A change in one particular fluid characteristic that has no effect at all on one type of device

may, in contrast, have a significant effect on another type of device. For

example, viscosity has two effects that are unique to a turbine flow

meter. Viscosity affects the flow profile and the boundary layer thickness

as the fluid flows over the turbine blades, resulting in non-linear performance. Viscosity also creates mechanical drag on the turbine bearing,

which impacts the resistance of the rotor to turn freely. Comparatively,

magnetic and Coriolis flow meters are less subject to viscosity changes,

but instead have other unique influence factors related to other fluid

characteristics.

Critical Fluid Characteristic. Device types have a single “Critical Fluid

Characteristic”, which is specific to each device type as defined by the

policies used for National Type Evaluation Program (NTEP) evaluations.

NTEP policies for grouping products according to key characteristics were

developed with input from State and Federal government officials, device

manufacturers, and other experts. These policies take into account meter

type and the effect of the different product characteristics on performance. For example, for mass flow meters, the critical fluid characteristic is

“specific gravity” because some mass flow meters use automatic density

correction to correct for changes in product density. A fluid with a significantly different specific gravity or density than the primary fluid would be

a poor substitute to use for testing. 

National Conference on Weights and Measures (NCWM) Publication 14

for Measuring Devices contains a valuable tool to help establish whether

or not one fluid should be substituted for another. The “Table of Product

Families for Meters” can be found in Part C of the Technical Policy in Publication 14. This table is organized to show what fluid products share the

same “Product Category” for a given type of meter. The table also shows,

in the definitions of the various tests, what the critical fluid characteristic

is for a meter type.

The “Critical Fluid Characteristics” for four different meter types are

shown in Table 1.

Table 1. 

Critical Fluid Characteristics by Meter Type 

as Determined by NCWM Publication 14 for Measuring Devices

The critical fluid characteristic can also be identified by consulting the

Mass Flow 

Meters

Magnetic Flow

Meters

Positive

Displacement

(PD) Meters

Turbine

Meters

Critical Fluid

Characteristics

Specific

Gravity

(Density)

Conductivity Dynamic

Viscosity

Kinematic

Viscosity
Calendar 2012

January 22 - 25

NCWM Interim Meeting

New Orleans, LA

Contact: info@ncwm.net

May 14 - 17

Northeastern Weights & Measures Association

(NEWMA)

Seekonk, MA

Contact: James Cassidy at

jcassidy@cambridgema.gov

CONTACTS FORWEBINARS

•Lab Metrology: Val Miller at val.miller@nist.gov or

view the Laboratory Metrology group webpage at: 

http://www.nist.gov/pml/wmd/labmetrology/webinars.cfm

•Devices: Tina Butcher at tina.butcher@nist.gov

•Laws & Metric: David Sefcik at david.sefcik@nist.gov

or Lisa Warfield at lisa.warfield@nist.gov

Additional details on the above calendar items

can be found at: 

http://ts.nist.gov/WeightsAndMeasures/calendar3.cfm

W&M Connection 4 Volume 2 Issue 3

June 6, 1755 - American patriot Nathan Hale

(1755 - 1776) was born. During the Revolutionary

War, he volunteered for a spy mission and was captured by the British. When brought before British

General William Howe, Hale admitted he was an

American officer. Howe ordered him hanged.

Hale’s famous last words, “I only regret that I have

but one life to lose for my country.”

June 10, 1652 - Massachusetts silversmith, John

Hull opened the first mint in America. This was in

violation of English colonial law. Hull designed the

first coin, which was called the Pine Tree Shilling.

June 14, 1775 - The 2nd Continential Congress established the first U.S. Military service consisting of

six companies of riflemen. By unanimous vote,

George Washington was made the Commander

of the army.

June 14, 1777 - John Adams made a resolution before Congress that stated, “that the flag of the thirteen stripes, alternate red and white; that the union

be thirteen stars, white on a blue field, representing

a new constellation.” Each year this event is celebrated in the United States as Flag Day.

June 20, 1782 - U.S. Congress officially adopted the

Great Seal of the United States.

MORE THIS MONTH IN HISTORY

NTEP Certificate of Conformance for a given meter or another meter of the

same type. The “Applications” section of the Certificate of Conformance

should state the range values for the critical fluid characteristic that are approved for a device based on previous NTEP testing and the application of

Technical Policy C.

Product Category Test Requirement Group. Product categories are defined as groups of products that have been shown to produce similar performance results for a given meter type. These categories were developed

to minimize the amount of testing required during NTEP evaluations intended to demonstrate meter performance with multiple products. Examples of product categories include fertilizers, crop chemicals, compressed

gases, compressed liquids, water, chemicals, fuels, solvents, and heated

products. 

Product categories are combined together in NCWM Publication 14 into

groupings that are defined by the type and extent of testing required.

These groupings are identified by the designation of the “test requirements.” There are six different test requirements named “Test A” through

“Test F.” Some test requirements apply only to certain device types. “Test

F” requirements apply only to magnetic flow meters, “Test C” requirements

apply only to positive displacement meters, “Test B” requirements apply

only to mass flow meters, and “Test E” requirements apply only to turbine

meters. Other test requirements apply to multiple device types. “Test D”

requirements apply to all device types and “Test A” requirements apply to

either turbine or positive displacement meters. The specific test requirements that apply in any given case will depend on both the device type and

the product.

Each of the six test requirements explain the grouping of product categories by describing what products are covered by the test requirements.

For example, “Test B” requirements state that “The Certificate of Conformance will cover all products in all product categories listed in the table

under Test B within the specific gravity range tested.” Because the coverage under “Test B” includes all products in all product categories under

“Test B”, then all “Test B” product categories fall into the same product

category test requirement group. This “Test B” product category test requirement group for mass flow meters was referred to collectively as “Normal Liquids” in 2010 and earlier editions of NCWM Publication 14. It is

valid to consider all the fluids in the “Test B” set of product categories as if

they were in a single product category for consideration of substitute fluids. Similarly, all the fluids in the various product categories that fall under

the “Test F” requirements should be considered as being in the same product category for magnetic flow meters when considering substitute fluids.

As another example, “Test E” requirements state that “The Certificate of

Conformance will cover all products in the product category within the

kinematic viscosity range tested.” Because the coverage under “Test E” includes all products in the product category, all “Test E” product categories

represent individual and separate product category test requirement

groups. Product category test requirement groups are separated by double lines in the Product Families Table in NCWM Publication 14 to help

readily identify these groupings. The product category test requirement

groups are structured such that the performance of a meter with a given

product will predict the performance and give results similar to those of

the meter with other products in that same product category test requirement group.

A product category test requirement group for one meter type will not

necessarily contain all the same fluids as it would for another meter type
IN THE FIELD

Is there a W&M topic that you would

like to have discussed in the Weights

and Measures Connection?

How can we better serve our W&M

community?

Do you have a safety tidbit to share?

Do you have a W&M event that you

wish to post in the Connection’s calendar?

Submissions can be sent to the Editor,

Linda Crown at linda.crown@nist.gov

W&M Connection 5 Volume 2 Issue 3

because, as noted in “Device Type” above, different meter types are affected by different fluid characteristics. The relationships between different fluids that determine whether they are in the same product category

for a given meter type or not are complex because they depend on similarities and differences in one or in many secondary characteristics. These secondary characteristics are other fluid properties, in addition to the critical

fluid characteristic, that can potentially impact test results for a given

meter type. Examples of secondary properties that help define product

categories include temperature range (as in the case of heated and cryogenic products), lubricity, phase stability, coefficient of thermal expansion,

vapor pressure, and solids content. The best way to ensure that test results

will not be impacted by a secondary characteristic of a substitute fluid is to

verify, using NCWM Publication 14, whether or not the two fluids share a

common product category test requirement group for a particular device. 

Consider as an example a case where water is proposed as a substitute

fluid for testing a device that has been installed to meter xylene. The

owner of the device is reluctant to run xylene for the start-up tests because

it is highly flammable and the testing arrangement will result in greater exposure and risk to safety than the normal system operation. NCWM Publication 14 reveals in the Product Families Table that xylene is in the product

category known as “Solvents General.” The “Solvents General” product category includes hexane, toluene, acetone, and some other solvents, but it

does not include water. Water would not be a good substitute for xylene if

the meter is either a positive displacement meter or a turbine meter because it is not in the same product category test requirement group as xylene. Although xylene is a “Test F” fluid for magnetic flow meters, water is

not a “Test F” fluid, so water would also not be a good substitute for a magnetic flow meter. For a mass flow meter, both xylene and water are fluids

in the same “Test B” product category test requirement group (formerly

known as “Normal Liquids”), so they can be considered as if they were in

the same product category, but only if the device were a mass flow meter.

The critical fluid characteristic for mass flow meters is specific gravity (density). The specific gravity of xylene is typically 0.89 and that of water is 1.0,

which are somewhat close together. If the NTEP certificate for the device

confirms in the “Applications” section that the meter approval already covers a range of specific gravities that includes both 0.89 and 1.0, then the

substitution may still be considered after consulting the manufacturer for

their input.

Other Fluid Characteristics Identified by the Manufacturer. Some device

designs have additional influence factors, identified by the meter manufacturer, that are related to certain particular fluid properties. In cases where

the meter manufacturer has identified influence factors related to fluid

characteristics beyond the critical fluid characteristic for that device type,

these other fluid characteristics must also be considered when evaluating a

fluid to use as a substitute for testing of that particular device. 

Once the fluid characteristics that can potentially influence the particular

device type are identified, the next task is to determine the degree to

which each of those characteristics may impact test results. The ideal scenario is for a substitute fluid to be equivalent to the primary fluid in every

characteristic that is known to have an influence on the device performance, but in many cases, small differences will arise that will make it necessary to determine if the magnitude of that difference is likely to influence

the outcome of the test.

An example of this would be the case where a device manufacturer has

published a secondary influence factor relating to pressure. To determine if

ANNOUNCING THE

NCWM 96TH ANNUAL MEETING

The 96th Annual Meeting for the National Conference on Weights and Measures (NCWM) will

take place Sunday, July 17 through mid day

Thursday, July 21, 2011. This year’s meeting

theme is “Educating Today for Tomorrow.” The

conference will take place in Missoula, Montana, which is surrounded by the majestic

Rocky Mountains and the Clark Fork River. 

The meeting agenda is provided in Publication

16, National Conference on Weights and Measures Committee Reports for the 96th Annual

Meeting, and is available online at:

http://www.nist.gov/pml/wmd/pubs/pub16-11.cfm

and http://ncwm.net/content/publication-16.

The NIST

Weights and Measures Division 

has a new homepage at: 

http://www.nist.gov/pml/wmd/index.cfm

Please change your 

browser’s bookmark.
W&M Connection 6 Volume 2 Issue 3

the effect of pressure on the device is likely to influence the outcome of

the test, first ascertain whether the substitute fluid would be measured at

a different pressure than the primary fluid. If this is the case, then use the

formula stated by the manufacturer to estimate the magnitude of the effect based on the expected difference in pressure between the substitute

fluid and the primary fluid. If the magnitude of this effect under the proposed test conditions with the substitute fluid would be significant in comparison with the allowed tolerance, then the proposed fluid would be a

poor substitute.

CONSULT DEVICE MANUFACTURERS

Whenever possible, the manufacturer of the device should be consulted

before approving a substitute test fluid. This can sometimes be achieved

simply by referring to their published specifications. It is not uncommon

for the published specifications of a measuring device to contain quantified

influence factors of field effects. Unfortunately, these effects are not always published or even well understood by all manufacturers, so the absence of these types of specifications cannot be interpreted as an absence

of any influence factors.

Ideally, the manufacturer should be contacted directly. If the manufacturer believes that the substitute fluid may have an effect on your test results, or is not sure of what the effects might be, then you should only

proceed with extreme caution. In order to avoid any misunderstanding

and possible wrong conclusions, the manufacturer should be provided with

the names and known properties of both the substitute fluid and the primary fluid. Additionally, you should provide the manufacturer with as

much information as is known about the test conditions and the normal

operating conditions (e.g., pressure, temperature, flow, etc.) since some of

these conditions may impact the characteristics of one or both of the fluids

differently in a way that affects performance of the device.

One other valuable piece of information that either the equipment owner

or the manufacturer may be able to provide is data from prior controlled

testing with the primary fluid. If the device model has been proven to perform within tolerances using the primary fluid at least once, then confidence in future testing using a qualified substitute fluid is higher than if

there is no historical data available involving the primary fluid.

AUTOMATIC TEMPERATURE-COMPENSATING SYSTEMS

In certain applications, automatic temperature compensation may be in

use. Automatic temperature compensation adjusts the indication and registration of a measured volume to the volume that the particular product

would occupy if it were at a specified reference temperature, typically

15 °C or 60 °F for petroleum products.

Substitution of another fluid in the testing of systems that include automatic temperature compensation is generally not recommended. The ultimate measurement accuracy of these types of systems depends on both

the accuracy of the primary flow measurement and the accuracy of the automatic temperature compensation system and its associated calculations.

Because the automatic temperature compensation system and its calculations are directly linked to the coefficient of thermal expansion (CTE) of the

primary fluid, it is highly likely that a substituted fluid with a different CTE

will have a significant impact on test results.

SUBSTITUTIONS FOR GASEOUS PRODUCTS

The same reasons that might exist to justify substitution of one liquid for

another during testing might also arise when metering gases. Since gases

NOW AVAILABLE,

THE NCWM 95TH

ANNUAL MEETING REPORT, 

SP 1115

The Annual Report from the 2010 meeting is

now available online at: 

http://www.nist.gov/pml/wmd/pubs/sp1115.cfm. 

In the next few weeks, the Reports of the National Conference on Weights and Measures

1905 - 2010 (SP 979) will become available.

This searchable DVD will be distributed by

mail to the NCWM membership. A limited

number of copies of this DVD will also be

available through the NIST Weights and

Measures Division by contacting Linda Crown

at Linda.Crown@nist.gov.

NOW AVAILABLE, THE NEW

HANDBOOK 133, CHECKING THE NET

CONTENTS OF PACKAGED GOODS

FOR 2011

The newly revised and formatted Handbook

133 is now available online for your immediate reference. The printed editions have arrived from the printer, and those who

requested a copy of the printed edition

through their National Conference on

Weights and Measures membership should

have received their copy. 

The free online edition is available here: 

http://www.nist.gov/pml/wmd/pubs/hb133-

11.cfm.

A listing of the amendments and editorial

changes are available at the above URL.

Visit the American Academy

of Pediatrics for Sun and

Water Safety Tips

http://www.aap.org/advocacy/releases/sum

mertips.cfm
W&M Connection 7 Volume 2 Issue 3

are more difficult to contain and control than liquids, this can be especially evident when the primary gas represents a

safety hazard because it is either toxic or flammable.

As in the case of liquids, NIST Handbook 44 also recognizes the substitution of gases for testing. In both Section 3.33.

“Hydrocarbon Gas Vapor-Measuring Devices,” paragraph N.1. “Test Medium,” and in Section 3.37. “Mass Flow Meters,”

paragraph N.2., the Handbook states that “The device shall be tested with air or the product to be measured.”

As more high pressure gaseous fueling applications (e.g., hydrogen) emerge, further attention needs to be given when

considering substitution of different gases during testing, primarily because of the highly dynamic nature of flows, pressures, and temperatures that are seen during high pressure gas fueling. The Joule-Thompson coefficient is a gas property

that indicates whether and by how much a gas will heat up or cool down as pressure changes and it can have dramatic

impacts on the temperature of a gas during test drafts. Different gases can behave entirely differently under otherwise

similar conditions.

THE BOTTOM LINE – WHO DETERMINES THE SUITABILITY OF A SUBSTITUTE LIQUID?

In the case of installation, start-up, and maintenance verifications of individual devices used in legal trade, the weights

and measures official has full jurisdictional authority and the final decision on whether a certain substitute fluid can be

used or not at their discretion. For Type Evaluation, any substitution of fluids is subject to the approval of the NTEP laboratories and the NTEP administrator.

For questions about this article or further information on product substitutions during testing of commercial measuring

devices, contact Marc Buttler by e-mail at marc.buttler@nist.gov or by phone at (301) 975-4615.

Happy 235th Birthday

America

Have a wonderful and safe

4th of July

From the NIST Photo Archive

In this photo: An inaccurate railroad scale could result in the

customer being under- or overcharged by a substantial

amount. Since 1913, NIST has worked with state weights and

measures offices and supplied them with accurate calibration standards traceable to the International System of Units

to ensure fairness in commerce and the uniformity of the

U.S. measurement system.

(Photo and content from NIST archives)