SPECIFICATIONS 

AND TOLERANCES 

for Reference 

Standards and 

Field Standard 

Weights and 

Measures

United States 

Department of 

Commerce 

Technology 

 Services 

National Institute 

of Standards and 

Technology

8. Specifications and Tolerances 

for Field Standard Weight Carts

NIST 

 Handbook

 2003 

105-8
 
SPECIFICATIONS 

AND TOLERANCES 

for Reference Standards and 

Field Standard 

Weights and Measures

8. Specifications and Tolerances for 

Field Standard Weight Carts

NIST Weight Cart Working Group 

Editor: 

Val Miller 

Henry V. Oppermann, Chief 

National Institute of Standards and Technology 

Weights and Measures Division 

Gaithersburg, MD 20899 

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

TECHNOLOGY ADMINISTRATION

Phillip J. Bond, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

Arden L. Bement, Jr., Director

October 2003

NIST 

 Handbook

 2003 

105-8
NIST Handbook 105-8 October 2003 i

Preface 

 Acknowledgement: 

The editor wishes to thank Ronald Balaze, Michigan Department of Agriculture and Georgia 

Harris, NIST Weights and Measures Division for their development of the first draft of this 

handbook in 1998. Thanks must be given the members of the NIST Weight Cart Working Group 

for their work in developing a standard for field standard weight carts. 

The working group included: 

Val Miller, NIST Office of Weights and Measures (Chair) 

Georgia Harris, NIST Office of Weights and Measures 

Bruce Adams, Minnesota Department of Commerce 

David Ehrnschwender, Fairbanks Scales, Inc. 

Emil Hazarian, Los Angeles County Agricultural Commissioner Weights and Measures Department 

John Dewald, Tiffin Loader Crane 

John Holt, Kanawha Scales and Systems, Inc. 

L.F. Eason, North Carolina Department of Agriculture and Consumer Services 

Richard Suiter, NIST Office of Weights and Measures 

Ronald Balaze, Michigan Department of Agriculture 

Sid Colbrook, Illinois Department of Agriculture Bureau of Weights and Measures 

Tom Schafer, Idaho Department of Agriculture Bureau of Weights and Measures 

Thanks must also be expressed to those members of the State Weights and Measures community 

who read the draft standard and provided constructive feedback to further improve the document. 

Without the input of potential users of field standard weight carts, this standard could not 

provide the balance between usability in the field and metrological integrity that has been 

achieved. 

The use of Field Standard Weight Carts in testing large capacity scales is a complex and 

sometimes emotional issue. Weight cart use permits one or two individuals to test a large 

capacity scale in a fraction of the time required by previous methods of testing. They allow the 

scale inspector or technician to load the weights required for the test into the weight cart and 

then move it to various positions on the scale deck, with a single handling of the weights. This 

results in tremendous time savings, which converts to similar savings in manpower costs and 

downtime for the scale operator. 

However, there are many sources of variability in weight carts used for scale calibrations. 

Variability sources include but are not limited to such items as consumable liquids used as fuel 

for liquid fueled engines, engine lubricating oil, hydraulic fluid, and also contamination by dirt, 

mud and/or water. There are also forces that are potentially destructive to the scale under test 

generated by the concentration of large amounts of weight on the small contact patch of rubbertired wheels. The members of the working group addressed each of these issues. 
NIST Handbook 105-8 October 2003 ii

Contents 

Preface .........................................................................................................................................................................i

Introduction ...............................................................................................................................................................1

1 Scope..................................................................................................................................................................1

1.1 ‘Field Standard’ Classification .................................................................................................................1

1.2 Retroactivity .............................................................................................................................................1

1.3 Safety Considerations ...............................................................................................................................2

1.4 Units .........................................................................................................................................................2

2 Reference Documents.......................................................................................................................................2

2.1 NIST .........................................................................................................................................................2

2.2 NCWM .....................................................................................................................................................3

3 Terminology......................................................................................................................................................3

4 General Specifications......................................................................................................................................3

4.1 Weight ......................................................................................................................................................3

4.2 Materials...................................................................................................................................................4

4.3 Workmanship, Finish, and Appearance ....................................................................................................4

4.4 Design.......................................................................................................................................................4

4.5 Identification Plate....................................................................................................................................4

4.6 Power........................................................................................................................................................5

4.7 Fuel Tank *..............................................................................................................................................5

4.8 Hydraulic Fluid System ............................................................................................................................9

4.9 Engine Lubricating Oil System.................................................................................................................9

4.10 Engine Exhaust.........................................................................................................................................9

4.11 Tires *.....................................................................................................................................................10

4.12 Wheel Bearings ......................................................................................................................................10

4.13 Minimum Wheelbase and Track Dimensions.........................................................................................10

4.14 Drainage .................................................................................................................................................10

4.15 Weight Restraint.....................................................................................................................................10

4.16 Weight Cart Transport ............................................................................................................................10

4.17 Lifting Attach Points...............................................................................................................................10

4.18 Adjustment Cavities................................................................................................................................11

4.19 Brakes.....................................................................................................................................................11

4.20 Directional Controls ...............................................................................................................................12

4.21 Battery * .................................................................................................................................................12

4.22 Battery Charging Circuit.........................................................................................................................12

4.23 Routine Lubrication................................................................................................................................12

4.24 Electrical Power Connections.................................................................................................................12

4.25 Remote Operation...................................................................................................................................12

5 Tolerances *....................................................................................................................................................13

Table 1. Tolerances..............................................................................................................................................13

6 Verification Requirements.............................................................................................................................13

6.1 Legal Requirements................................................................................................................................13

6.2 Initial Verification ..................................................................................................................................13

6.3 Periodic Calibration................................................................................................................................14

6.4 Traceability.............................................................................................................................................14

6.5 Calibration Reports.................................................................................................................................14
NIST Handbook 105-8 October 2003 iii

7 Test Methods ..................................................................................................................................................14

7.1 Documented Test Procedure...................................................................................................................14

8 Uncertainties...................................................................................................................................................14

9 User Requirements.........................................................................................................................................15

9.1 Use In Combination With Test Weights.................................................................................................15

9.2 Weight Cart Maintenance.......................................................................................................................15

9.3 Weight Cart Maintenance Log................................................................................................................15

9.4 Inspection Checklist Verification ...........................................................................................................15

9.5 Weight Cart Cleanliness .........................................................................................................................16

9.6 User Modifications .................................................................................................................................16

9.7 Licensing of Weight Cart Operators (Informational).............................................................................16

Figure 1 Typical Liquid Fuel Powered Weight Cart Configurations..................................................................17

Figure 2 Typical Electrically Powered Weight Cart Configurations ..................................................................18

Attachment 1 Example Fuel Tank Drawing.........................................................................................................19

Attachment 2 Example Daily Weight Cart Inspection Checklist........................................................................20
NIST Handbook 105-8 October 2003 1

Specifications and Tolerances 

 for Reference Standards and Field Standard 

 Weights and Measures 

8. Specifications and Tolerances for Field Standard Weight Carts 

These specifications and tolerances are recommended as minimum requirements for standards 

used by State and local weights and measures officials and others in the verification of large 

capacity scales used in quantity determination of commodities by means of weighing. 

Key words: weight cart; retroactivity; field standard weight cart; specification; standard; 

scale; tolerance; scale specifications and tolerances; weights and measures. 

Introduction 

A field standard weight cart (after this, simply called "weight cart") is intended for use in 

conjunction with Class F weights for testing commercial weighing devices for compliance with 

the requirements of NIST Handbook 44. The combination of Class F weights and weight cart 

may be used to test class III and III L scales with a division size (‘d’) equal to or greater than 5 

lb, class IIII scales, and scales not marked with a class designation with a ‘d’ equal to or greater 

than 5 lb. 

Compliance with this standard does not guarantee suitability of a weight cart to test a specific 

weighing device at all specified test loads. Each test load to be used must be evaluated for 

compliance with the requirements of NIST Handbook 44, Appendix A, “Fundamental 

Considerations,” Section 3, “Testing Apparatus.” This section of Handbook 44 establishes the 

minimum requirements for the standards used in legal metrology, including a statement that the 

maximum error of an uncorrected standard should not exceed one-third of the smallest tolerance 

for the device tested.1 

1 Scope 

1.1 ‘Field Standard’ Classification 

These specifications are limited to motorized weight carts used in conjunction with NIST 

Handbook 105-1, Class F field standard weights. Weight carts are NOT considered NIST Class 

F field standards. This handbook does not apply to railroad test cars or non-motorized weight 

baskets. 

1.2 Retroactivity 

These specifications apply to new weight carts manufactured after the effective date of this 

publication (September 2003). 

A weight cart in service before the publication of this standard that maintains tolerance between 

verification tests shall continue to be acceptable, though some modifications may be required for 

 

1

 Equation to be used: 3

T T T scale cart + weights <
NIST Handbook 105-8 October 2003 2

continued acceptability under this standard. All weight carts in service must comply with those 

specifications that have an asterisk (*) following the title. These include requirements 

addressing tires, batteries, tolerances and fuel tanks. Existing components that comply with the 

requirements are acceptable for continued use. Weight carts in service at the time of this 

publication that do not conform to required sections, must be brought into compliance by 

December 31, 2005. 

Weights and measures jurisdictions may require that a weight cart comply with non-retroactive 

specifications, if additional modifications are required to maintain a weight cart within tolerance. 

Weight carts that do not maintain the specified tolerance shall be removed from service until 

modifications are performed that enable the weight cart to maintain tolerance. 

1.3 Safety Considerations 

The use of weight carts may involve hazardous materials, conditions, operations and equipment. 

This document does not purport to address the safety problems associated with weight cart use. 

Known hazards may include, but are not limited to: 

- The handling of petroleum products, 

- The handling and connection or disconnection of energized electrical cables, 

- The use, maintenance and disposal of various types of batteries, 

- Handling of large weights, and 

- Possible exposure to carbon monoxide fumes from gasoline engine exhaust. 

It is the responsibility of the user to establish appropriate safety and health practices and to 

determine the applicability of regulatory limitations prior to use. 

1.4 Units 

The majority of scales tested with weight carts indicate mass values in U.S. Customary units. 

Petroleum products used in weight carts have a 60 °F (15.56 °C) reference temperature. 

Therefore, this publication primarily uses U.S. Customary units due to the needs of industry and 

regulators. Metric equivalents are provided when the likelihood exists that they may be used. 

Metric equivalent values provided may not be exact conversions but are provided as convenient 

alternative values that will not have an adverse impact on the quality of the scale calibrations. 

2 Reference Documents 

2.1 NIST2

NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for 

Weighing and Measuring Devices, (current edition) 

NIST Handbook 105-1, Specifications and Tolerances for Field Standard Weights (NIST Class 

F) 

NIST Handbook 112, Examination Procedure Outlines for Weighing and Measuring Devices 

 

2 NIST, National Institute of Standards and Technology
NIST Handbook 105-8 October 2003 3

2.2 NCWM3

NCWM Publication 3, NCWM Policy and Guidelines, Section 3.2.15, 1991. 

NCWM Publication 14, National Type Evaluation Program, (NTEP) Administrative Procedures, 

Technical Policy, Checklists, and Test Procedures, see current edition, published annually. 

3 Terminology 

Class F Field Standard Weight. A weight meeting NIST Handbook 105-1 design, construction 

and tolerance criteria for field standards. 

Field Standard. The term “field standard” means the physical standards that meet specifications 

and tolerances in NIST 105-series handbooks (where available) having calibrated measurement 

results traceable to primary or secondary standards through comparisons using accepted 

laboratory procedures. 

Tolerance. Maximum permissible error. A value fixing the limit of allowable error or departure 

from the true performance or value. 

Tcart. Tolerance of empty weight cart. 

Tweights. Tolerance for NIST Class F field standard weights used to supplement the weight cart to 

achieve a given test load in scale testing, from NIST HB 105-1. 

Tscale. Tolerance of the scale at the test load, from HB 44. 

Weight cart. A field standard test weight meeting the requirements of NIST Handbook 105-8 

used both as a field standard weight and as the means of moving NIST Class F field standard 

weights before, during and after, large capacity scale tests. 

4 General Specifications 

4.1 Weight 

4.1.1 Nominal Empty Weight 

Weight carts shall be constructed in one of the following 500 lb (226.80 kg) increments: 2000 lb 

(907.18 kg), 2500 lb (1133.98 kg), 3000 lb (1360.78 kg), 3500 lb (1587.57 kg), 4000 lb (1814.37 

kg), 4500 lb (2041.17 kg), 5000 lb (2267.96 kg), 5500 lb (2494.76 kg) or 6000 lb (2721.55 kg). 

Suitability for the intended application should be considered before selecting a nominal value. 

The weight cart, with the adjustment cavity empty and all fluid levels adjusted to the reference 

levels, shall weigh a minimum of 50 lb and a maximum of 100 lb less than the nominal empty 

weight. 

 

3 NCWM, National Conference on Weights and Measures 
NIST Handbook 105-8 October 2003 4

The manufacturer will supply each new weight cart with sufficient adjustment material to bring 

the weight cart to its nominal mass. 

4.1.2 Weight and Size Limitations 

Local weights and measures jurisdictions may have use, size or weight restrictions on weight 

carts. Approval of use, size and weight must be obtained from the weights and measures 

jurisdiction(s) in which weight cart use is planned. Coordination between the purchaser and the 

supporting calibration laboratory is essential, before purchase, to ensure that the laboratory can 

provide a proper calibration. 

4.2 Materials 

A weight cart body and frame shall be constructed of steel. Other durable and stable materials 

may be developed, but approval for use of such materials must be obtained from the NIST 

Weights and Measures Division or local Weights and Measures agency prior to use of alternative 

construction materials. 

Rubber hoses may be utilized for fluid transfer where flexible connections are needed, but 

should be kept to a minimum. Metallic tubing is to be used where possible to minimize use of 

rubber hoses. 

4.3 Workmanship, Finish, and Appearance 

All edges and corners shall be smooth, with no sharp edges, to prevent injury during routine use 

and maintenance. All surfaces shall be free from slag, scale and weld splatter, grit, dirt, or any 

foreign matter before shipment from the factory or before submission for calibration. 

Unless constructed of corrosion resistant materials, all exposed surfaces shall have a protective 

surface coating. The coating must be a high quality material having the following properties: 

corrosion inhibiting, chip and abrasion resistant, smooth surface and non-hygroscopic. Flat 

aluminum paint or flat lacquer finishes are preferred. 

4.4 Design 

Representative designs are shown in Figures 1 and 2; variations in design are permitted. Prior to 

production, manufacturers should seek design approval from NIST Weights and Measures 

Division. ‘Design approval’ applies only to the size and suitability of the cart as a field standard 

in the calibration of large capacity scales, and will not in any way imply design approval for 

structural strength and integrity. 

4.5 Identification Plate 

4.5.1 Placement 

Each weight cart shall have an identification plate permanently mounted in a conspicuous and 

easily accessible place near the operator controls. 
NIST Handbook 105-8 October 2003 5

4.5.2 Content 

The identification plate shall contain the following items in clear permanent text in a font size no 

smaller than 0.1 in by 0.1 in (2.5 mm by 2.5 mm). 

- Nominal empty weight of the cart; 

- Maximum gross weight; 

- Name and address of the manufacturer; 

- Manufacturer’s model number; 

- Manufacturer’s unique serial or identification number; 

- Date of manufacture; 

- Statement of compliance with NIST HB 105-8 including the revision in effect at time of 

manufacture; and 

- Additional information that the manufacturer may deem necessary. 

4.6 Power 

Weight carts may be powered by an electric motor (battery or generator driven), or liquid fueled 

engine. Power may be transmitted to the wheels by either fluid or mechanical coupling methods. 

4.7 Fuel Tank * 

4.7.1 Capacity, Shape and Mounting 

Liquid fueled weight carts shall have a maximum total fuel capacity of 1-gallon (231 in3 or 3785 

cm3

) when filled to the fuel tank reference level. Of this volume, a minimum of 0.72 gallons 

(167 in3 or 2740 cm3) shall cause an indication in the sight gauge. The fuel tank shall have the 

general shape of an upright cylinder and shall comply with all applicable state and federal 

regulations. The fuel tank shall be permanently attached to the weight cart structure so that the 

gauge assembly is positioned vertically. The fuel tank shall be mounted on the weight cart 

structure away from heated components such as the engine exhaust so that refueling does not 

constitute an unnecessary safety hazard. The top of the fuel tank, when mounted to the weight 

cart, shall not extend above the plane described by the top edge of the weight restraint system. A 

representative fuel tank design is shown in Attachment 1; approved variations of this design are 

permitted. Prior to production, manufacturers should obtain the approval of the NIST Weights 

and Measures Division for new fuel tank designs. New designs should be submitted to the 

Weights and Measures Division, National Institute of Standards and Technology, Gaithersburg, 

MD 20899. 

The fuel tank shall be identified with a unique serial number permanently etched or stamped into 

the tank near the fill cap 

4.7.2 Cross Sectional Area of Tank 

The combined cross sectional area of the fuel tank and sight gauge must be no greater than 

12.8 in2

 (82.33 cm2) at all liquid levels within the graduated range. 

4.7.3 Fuel Tank Material 

The fuel tank shall be constructed of low carbon or corrosion resistant steel. Non-integral 

hardware may be constructed of other materials provided the material is durable and suitable for 

its intended purpose. 
NIST Handbook 105-8 October 2003 6

4.7.4 Fuel Tank Color and Finish 

The fuel tank shall be light in color to minimize heating of the fuel by radiant heat sources. Any 

plating or paint materials shall not be degraded by contact with the fuel. A natural stainless steel 

color is acceptable. 

4.7.5 Fuel Tank Drain 

If the fuel tank is equipped with a fuel tank drain apparatus, the assembly must extend past the 

edge of any nearby weight cart structure. 

4.7.6 Gauge Assembly 

4.7.6.1 Gauge Tube 

4.7.6.1.1 Material 

Weight cart fuel tanks shall be equipped with a (liquid-level) gauge tube mounted on the tank 

body in plain view of the weight cart operator. The gauge tube shall be made of a transparent 

material such as borosilicate glass, be clear and free of any markings, irregularities or defects 

which will distort the appearance of the liquid surface. Clarity of the gauge tube material shall 

not be degraded by contact with the fuel. The gauge tube may be coated to prevent fuel spillage 

in case of tube breakage, provided the coating material is clear and free of markings, 

irregularities or defects that will distort the appearance of the liquid surface and is not degraded 

by contact with the fuel. 

4.7.6.1.2 Mounting 

The gauge tube shall be mounted in fittings which penetrate the tank body near the base and as 

near the top as possible (to allow passage of vapors from the tube for vapor recovery purposes). 

Fittings shall be designed so that all fuel and vapor are returned to the fuel tank and no spillage 

can occur. The fitting at the top of the tube may have a removable plug so the tube can be 

cleaned. However, this plug opening must be sealed during weight cart operation. The plug 

shall not interfere with proper vapor equalization (i.e., it shall not allow pressure build up to 

affect the liquid level in the gauge). Removal and replacement of the tube shall be possible and 

the metal to glass seal shall be made leak proof by the use of compressible gaskets or "O" rings. 

4.7.6.2 Shield 

On fuel tanks where protection of the tube is provided by a shield or cover, the design of the 

cover shall allow replacement of the gauge tube with ease and shall facilitate gauge reading by 

the weight cart operator. 

4.7.6.3 Scale Plate and Graduations 

4.7.6.3.1 Material 

The scale plate shall be rigid and resistant to corrosion and discoloration (anodized aluminum or 

stainless steel). 

4.7.6.3.2 Location 

The scale plate shall be mounted on a secant to the front of, or slightly in front of the gauge tube. 

In no case shall the scale plate be more than 0.25 in (6 mm) from the tube. 

 
NIST Handbook 105-8 October 2003 7

4.7.6.3.3 Mounting 

There shall be a sufficient number of scale brackets (minimum of two) to hold the scale plate 

rigidly in place. The scale plate shall be securely attached to the brackets and be provided with a 

means for sealing. 

4.7.6.3.4 Scale Units 

The basic units on fuel tank scale plates shall be pounds of fuel, based on the average density of 

the fuel used at the API4 reference temperature of 60 °F (15.56 °C). The reference density to be 

used5: Gasoline: 6.213 lb/gal (API 58.38), and diesel: 7.113 lb/gal (API 34.35). The scale plate 

shall be clearly marked as to the unit of measure with the header text “Add lb.” to indicate the 

amount of weight required to return the weight cart to its nominal weight with the indicated fuel 

load. Graduated scale plates shall be made of a single piece of material and adjusted and sealed 

as a unit. 

4.7.6.3.5 Graduation Spacing 

The minimum distance between adjacent graduation lines shall be 0.0625 in (2 mm), and the 

lines shall be evenly spaced. 

4.7.6.3.6 Span of Graduations 

The sight gauge scale plate shall be graduated at a reference (zero) line with major graduations at 

0.5 lb increments with sub-graduations at 0.25 lb increments below the reference line, over the 

length of the sight gauge. The reference line shall be approximately 1 inch from the top of the 

gauge tube. The distance between the markings shall be established based on the fuel tank crosssectional area and the API value for the recommended fuel. 

4.7.6.3.7 Scale Lines 

The graduation lines, numbers, and other inscriptions on the scale plate shall be engraved, etched 

or silk screened, permanent, and of a contrasting color to that of the plate. 

4.7.6.3.8 Line Spacing and Width 

Major graduation lines, consistent with the measurement system used, shall be longer than 

sub-graduation lines and shall be appropriately numbered. The length of the major (numbered) 

graduation lines on the scale plate shall be no less than 0.25 in (6 mm), and the sub-graduation 

lines shall be no less than 0.125 in (3 mm) in length. All lines shall extend to the edge of the 

scale plate nearest the gauge tube. Graduation lines shall be of uniform width and not more than 

0.025 inches (0.6 mm) or less than 0.015 inches (0.4 mm) wide. 

4.7.6.3.9 Volume Reference Marking 

The reference volume line on the scale plate shall extend across the entire width of the scale 

plate and shall be clearly identified. Each 0.5 lb graduation shall be appropriately labeled to 

indicate the mass of the fuel required to return the fuel level to the reference line. 

 

4 American Petroleum Institute 

5

 Based on 2001-2002 fuel data obtained from Northrop Grumman Petroleum Technologies, Bartlesville, OK 
NIST Handbook 105-8 October 2003 8

4.7.6.3.10 Additional Markings 

Scale plates shall be clearly marked with the fuel tank manufacturer’s name, the fuel tank serial 

number, type of fuel and fuel density (lb/gal) for which it is intended. Letters and numbers shall 

be legible and of adequate size, not less than 0.1 inches (2.5 mm) in height. 

4.7.7 Tolerances (Maximum Permissible Error) 

The difference between the actual volume and any indicated volume at the prescribed reference 

temperature, 60 °F (15.56 °C), shall not be greater than ± 2 in3 (32.8 cm3) based on the assumed 

reference fuel density as stated in section 4.7.6.3.4. 

4.7.8 Fuel Tank Initial and Periodic Verification 

Weight cart fuel tank scale plate graduations must undergo initial verification for conformance to 

these specification and tolerances during the initial calibration of the weight cart, prior to placing 

the weight cart into service, and when damage is suspected. Routine calibration of the fuel tanks 

is not recommended. Initial fuel tank verification may be conducted by the fuel tank or weight 

cart manufacturer provided a certificate of conformance to the applicable sections of NIST HB 

105-8 is provided with the fuel tank. The fuel tank certificate of conformance must indicate the 

fuel tank manufacturer’s name and address, fuel tank serial number, the standard(s) used for 

calibration, the expanded uncertainty of the calibration process, a statement of measurement 

traceability, and identification of the individual performing the verification. The fuel tank 

conformance certificate shall become part of the weight cart maintenance log. 

NOTE: The described certificate of conformance does not meet the requirements of ISO/IEC 

17025 for an accredited calibration. An accredited calibration of the weight cart may require that 

an accredited laboratory perform the one-time fuel tank verification.

4.7.9 Fuel Tank Verification Method 

Verification to determine whether a weight cart fuel tank meets applicable tolerances is 

performed by calibration using accepted volumetric calibration procedures. The uncertainty of 

the test method must be less than one-third of the tolerance. 

4.7.10 Fuel Level Error Weights 

The manufacturer of a liquid fueled weight cart shall supply sufficient 0.5 lb error weights (and a 

separate carrying case) to compensate for the fuel tank capacity visible on the sight gauge. A 

means shall be provided (e.g., a basket or hook arrangement) whereby the operator can easily 

and securely attach the 0.5 lb error weights to the weight cart structure to compensate for weight 

lost as liquid fuel is expended. The mounting arrangement shall securely restrain the Fuel Level 

Error Weights to prevent them from vibrating. The error weights shall be placed on the weight 

cart structure only when required to compensate for expended fuel. The Fuel Level Error 

Weights shall conform to tolerances and specifications contained in NIST Handbook 105-1, 

“Specifications and Tolerances for Field Standard Weights (NIST Class F).” 
NIST Handbook 105-8 October 2003 9

4.8 Hydraulic Fluid System 

4.8.1 Hydraulic Fluid Reservoir Fluid Level Indicator 

Weight carts equipped with a hydraulic reservoir must have a sight gauge, with a clearly marked 

reference level, for maintaining hydraulic fluid levels. The fluid level must be visible under all 

operating conditions. The hydraulic reservoir shall have sufficient expansion capacity so that no 

hydraulic fluid will be lost during normal use. The fluid level shall be adjusted to the reference 

level with the hydraulic fluid temperature at calibration laboratory conditions (18 °C to 27 °C). 

4.8.2 Hydraulic Fluid Reservoir Fluid Fill and Drain Tamper Indicators 

The fill and drain caps of the hydraulic reservoir shall be equipped so that a wire seal can be 

installed to indicate tampering with or adjustment of the hydraulic fluid level. Tampering or 

adjustment requires that the weight cart be submitted for recalibration prior to use as a field 

standard. 

 

4.8.3 Hydraulic Fluid Reservoir Fluid Drain System 

If equipped with a hydraulic fluid reservoir drain apparatus, the drain assembly must extend past 

the edge of any nearby weight cart structure. 

4.8.4 Hydraulic Fluid Filtration System 

The hydraulic fluid filter system shall be positioned, or a suitable means developed, so that 

removal does not cause oily contamination of any fixed cart surfaces. 

4.9 Engine Lubricating Oil System (if equipped with an internal combustion engine)

4.9.1 Engine Lubricating Oil Reservoir Reference Level 

The lubricating oil reservoir of the weight cart engine shall be maintained at the reference level 

established by the engine manufacturer using the recommended lubricating oil type. The 

lubricating oil level shall be adjusted, prior to calibration or use, to the reference level with the 

oil temperature between 18 °C and 27 °C (64 °F and 81 °F ). The engine must not have been 

operated for a period of at least 4 hours immediately prior to adjustment of the engine oil level. 

Significant contamination by fuel or combustion deposits shall require that the lubricating oil be 

replaced and that the cart be recalibrated. 

4.9.2 Engine Lubricating Oil Reservoir Drain System 

If equipped with a lubricating oil reservoir drain apparatus, the drain assembly must extend past 

the edge of any nearby weight cart structure. 

4.9.3 Engine Lubricating Oil Filter 

The engine oil filter shall be positioned, or a suitable means developed, so that removal does not 

cause oil contamination of any fixed cart surfaces. 

4.10 Engine Exhaust 

The exhaust pipe(s) shall be positioned and/or shielded so that the operator does not come in 

contact with them during normal weight cart operation. Exhaust gasses shall exit the exhaust 

pipe(s) in a horizontal direction and shall be directed away from the operator control station. 
NIST Handbook 105-8 October 2003 10

4.11 Tires * 

4.11.1 Size and Number 

Tire size and quantity shall be chosen to prevent scale platform contact pressures that exceed 

design limitations. The total contact area of the tires to the supporting surface shall cause no 

point load concentrations in excess of 200 lb/in2

 (1.38 MPa) when loaded to the maximum gross 

capacity of the weight cart. 

4.11.2 Tire Tread Pattern 

Weight cart tire surfaces shall be smooth (without tread) and have no major cuts or deformations. 

4.12 Wheel Bearings 

Axle bearing/hub assemblies should not require routine lubrication. Where possible, the use of 

sealed prelubricated bearings is recommended. Bearing units requiring liquid lubricants are not 

permitted. 

4.13 Minimum Wheelbase and Track Dimensions 

The weight cart shall be designed so that the center of gravity in any loading configuration shall 

not cause the weight cart to become unstable on slopes normally encountered during scale 

testing. 

4.14 Drainage 

Weight carts shall be designed to prevent the pooling of water on weight cart surfaces. 

Horizontal surfaces of the cart must be constructed of a single layer of material to prevent weight 

instability caused by trapped water layers. 

4.15 Weight Restraint 

Weight carts shall be permanently equipped with a weight restraint system suitable for the 

weights being used to restrain all test weights being transported during scale testing. 

4.16 Weight Cart Transport 

It is strongly recommended that weight carts be transported in an enclosed truck body to prevent 

contamination of the weight cart. As a minimum, the weight cart shall be covered by a suitable 

waterproof covering during transport. The weight cart shall have provision to be securely 

fastened to the transporting vehicle while being transported. 

4.17 Lifting Attach Points 

4.17.1 Lifting Attach Points Purpose 

The weight cart shall be equipped with a means of lifting the empty weight cart onto a transport 

vehicle and onto a scale or balance for calibration. 

4.17.2 Weight Cart Balance 

The empty weight cart shall balance in an approximately level position when lifted by the means 

specified by the manufacturer. 
NIST Handbook 105-8 October 2003 11

4.18 Adjustment Cavities 

Weight carts shall be designed with one or more adjustment cavities. Multiple adjustment 

cavities are permitted when required for adjusting the balance of the weight cart when lifted in 

the manner specified by the manufacturer. Adjustment cavities must be designed to prevent 

water penetration/contamination. 

4.18.1 Cavity Capacity 

Weight cart adjustment cavities shall have a minimum total capacity of approximately 150 lb of 

adjustment material. 

4.18.2 Adjustment Cavity Mounting 

Adjustment cavities must be removable for performing weight adjustment activities. Adjustment 

cavities shall be securely attached to the main weight cart structure and configured so that a wire 

seal or other suitable tamper indicator can be installed to indicate tampering. 

4.18.3 Adjustment Cavity Opening(s) 

Adjustment cavity opening(s) shall be easily accessible, sufficiently large and positioned to 

facilitate the insertion and removal of adjustment materials. Adjustment cavity openings shall be 

watertight. 

Each adjustment cavity opening shall have provision for sealing with a wire seal, or other 

suitable seal to indicate tampering. 

4.18.4 Adjustment Material 

Any metal in the form of shot or solid pieces may be used in adjustment cavities to adjust the 

weight of the cart. Lead or steel shot is preferred. Molten metals are not permitted. 

4.19 Brakes 

4.19.1 Service Brake 

Weight carts shall be designed with a braking device or system that allows the operator to 

restrain the fully loaded cart when descending slopes, and to bring the weight cart to a smooth 

stop when desired. The service brake must maintain the weight cart in position until released by 

the operator. 

4.19.2 Parking Brake 

Weight carts shall be designed with a parking brake that engages automatically when the engine 

stops, or that the operator may engage manually, to prevent undesirable weight cart motion. The 

parking brake must be capable of restraining the cart at the maximum gross weight under normal 

operating conditions. 

The parking brake and service brake may be the same system, provided both functions are 

performed. 
NIST Handbook 105-8 October 2003 12

4.20 Directional Controls 

All operator controls shall be permanently and unambiguously labeled as to the expected weight 

cart response with an indicated operator input. 

4.21 Battery * 

Batteries used to provide power to the motor for starting or propulsion shall be of the sealed lead 

acid type. The battery shall be placed for ease of maintenance and have a means of installing a 

wire seal to indicate tampering, adjustment or replacement. The wire seal must be placed to 

allow safety inspections and routine maintenance such as terminal cleaning. The weight cart 

must be submitted for recalibration if the battery is replaced. 

4.22 Battery Charging Circuit 

The battery charging circuit shall regulate the charging voltage and current at a level suitable for 

the battery in use to avoid mass instabilities caused by venting through the battery case pressure 

relief mechanism. 

4.23 Routine Lubrication 

All lubrication points must be accessible from a safe location around the cart while it is parked 

on a flat surface. Routine maintenance shall not require that the weight cart be suspended from a 

hoist to perform routine lubrication. The design shall allow easy removal of excess or displaced 

lubricant after servicing. 

4.24 Electrical Power Connections 

External electrical power required by weight carts with electric motors shall be supplied via a 

detachable power cord from either a truck mounted generation system or from facility power. 

The power connections shall be made using electrical connectors that are Underwriters 

Laboratories approved and that conform to local electrical codes. It is recommended that 

electrical code requirements be investigated prior to manufacture of the cart. 

Only those electrical connectors permanently mounted to the weight cart structure shall be 

included in the calibrated mass of the weight cart. All removable electrical connectors shall be 

removed during calibration and at any time when the calibrated mass of the weight cart is 

referenced or used. 

Any upgrades or changes required by changes in the local electrical code requires that the weight 

cart be submitted for recalibration prior to use. 

4.25 Remote Operation 

Remote operation of the weight cart may require the addition of actuators and radio frequency 

receiving units. The installation of such components shall not interfere with compliance with 

this handbook. 
NIST Handbook 105-8 October 2003 13

5 Tolerances * 

The tolerances in Table 1 are the maximum allowed if the standard is to be used without 

correction in scale testing applications. Weight carts should be adjusted during calibration to 

nominal values when possible. 

Table 1. Tolerances 

Nominal Empty 

Weight 

(lb) 

Weight Cart 

Tolerance 

(± lb) 

2000 0.50 

2500 0.50 

3000 1.00 

3500 1.00 

4000 1.25 

4500 1.25 

5000 1.50 

5500 1.50 

6000 2.00 

The assigned weight cart tolerances are based on an evaluation of the expanded uncertainty of 

the scale calibration as compared with one third of the current scale maintenance and acceptance 

tolerances (from NIST Handbook 44 tolerance tables applied to the device being tested). The 

sum of the maximum allowable error of the weight cart plus the allowable errors of the weights 

required to perform the test shall be used to evaluate test loads for compliance to Handbook 44 

requirements. 

6 Verification Requirements 

6.1 Legal Requirements 

The specifications and tolerances specified in this handbook are intended to permit the use of 

weight carts in normal field-testing operations as field standards having nominal values. 

Weights and measures requirements, including but not limited to, inspection, testing, and 

sealing, by a NIST WMD Recognized laboratory shall be followed. 

NOTE: Some States have requirements that are not documented here. Check with your local 

jurisdiction for requirements. 

6.2 Initial Verification 

A weight cart shall be inspected and calibrated before being placed in service to ensure that the 

specifications and tolerances of this handbook are met. The calibration status of a weight cart 

shall be verified as often as required by regulation or circumstance, especially when damage is 

known or suspected. 
NIST Handbook 105-8 October 2003 14

6.3 Periodic Calibration 

Field standards must be verified prior to use and rechecked as often as regulations or 

circumstances require, especially when damage is known or suspected or seals are broken. 

Initial weight cart calibration intervals shall be established at 1 year and extended or reduced 

based on historical evidence, up to the limit determined by State or local regulations. The 

calibration interval should not exceed 2 years due to the many variable mass components. 

6.4 Traceability 

Field standards used for legal metrology must be traceable to national standards by calibration in 

a laboratory recognized under the NIST WMD Laboratory Recognition Program to calibrate in 

that parameter, range, and scope or a calibration laboratory authorized by a W&M jurisdiction to 

calibrate field standards. 

All components of the weight cart that are not an integral part of the structure shall be sealed to 

the weight cart structure by means of a wire seal or by use of a tamper indicating material such as 

an inspection seal lacquer. These include but are not limited to: the battery, motor, hydraulic 

pump, fluid fill caps, drive motors and oil filter. Removal or replacement of any of these items 

shall be recorded in the maintenance log of the weight cart. 

6.5 Calibration Reports 

Acceptable accuracy and traceability to national or international standards shall be documented 

in a calibration report meeting the requirements of NIST Handbook 143, State Weights and 

Measures Laboratories Program Handbook. 

An ‘Inspection Checklist’ must accompany the Calibration Report for all weight carts. (See 

sample checklist in NIST Handbook 145, SOP 33, “Recommended SOP for Calibration of 

Weight Carts”). 

7 Test Methods 

7.1 Documented Test Procedure 

Calibration of weight carts shall be by an approved NIST procedure, NIST Handbook 145, SOP 

33, “Recommended SOP for Calibration of Weight Carts.” Additional requirements may be 

established by the jurisdiction in which the weight cart will be used. 

8 Uncertainties 

Uncertainties of the calibration must be evaluated according to the ISO Guide to the Expression 

of Uncertainty in Measurement, 1993. The expanded uncertainty (k=2) of the calibration must 

be less than one-third of the tolerance specified for the weight cart being tested and be evaluated 

to ensure that the three to one accuracy ratio required by NIST Handbook 44 is maintained. 

Typical uncertainty components for calibration that should be considered are: scale/balance 

standard deviation, uncertainty of standards and such other measurement influences that are 

determined to be significant to the weight cart calibration process. 
NIST Handbook 105-8 October 2003 15

9 User Requirements 

9.1 Use In Combination With Test Weights 

A weight cart may be used, alone or in combination with Class F field standard weights, up to 

the maximum gross weight established by the manufacturer. The user must ensure that the 

requirements of NIST HB 44 are maintained. Compliance with NIST HB 105-8 does not 

guarantee suitability of a weight cart to test a specific weighing device at all test loads. Each test 

load must be evaluated for compliance with the requirements of NIST Handbook 44, Appendix 

A, “Fundamental Considerations,” Section 3, “Testing Apparatus.” The combined tolerance of 

the weight cart plus the tolerance of any weights used on the cart must be less than one-third of 

the scale tolerance to be applied 















+ <

3

scale T

weights T cart T . This determination of suitability is 

especially critical for testing Class III scales, having division sizes ‘d’ = 5 lb or ‘d’ = 10 lb, to 

acceptance tolerances. 

9.2 Weight Cart Maintenance 

Any maintenance process performed between scheduled calibrations altering the mass of the 

weight cart invalidates the calibrated mass of the cart and requires that the weight cart be 

recalibrated. This includes, but is not limited to: replacement of the battery, changing lubricating 

oil and filter, and servicing of the hydraulic system. When “As Found” data is required for 

reverse traceability, maintenance should be performed after measuring and recording the “As 

Found” mass of the weight cart. For this test, only the fuel level shall be adjusted. All other 

fluid levels shall remain as they were when the cart was delivered for calibration. “Final” 

calibration data shall be recorded after completion of routine maintenance, adjustment of all fluid 

levels, and any other adjustments. 

9.3 Weight Cart Maintenance Log 

The organization owning the weight cart shall establish a maintenance log containing a detailed 

record of all maintenance performed on the weight cart. The log should document serial 

numbers of individually serialized weight cart components, e.g. engine, hydraulic pump, battery 

and drive motors. The log will include copies of all Calibration Reports and completed 

Inspection Checklists, as well as fuel tank conformance certificates, if appropriate. This log 

shall document the calibration status and history of the weight cart beginning at the time of 

initial placement in service to the current time of use. The Maintenance Log of weight carts 

placed in service prior to publication of Handbook 105-8 shall begin as of the date of Handbook 

105-8 publication and shall include such previous documentation as is available. Documentation 

of maintenance shall include a description of the maintenance performed, including part numbers 

and serial numbers where applicable, and when available, the weight of items removed from or 

installed on the weight cart. 

9.4 Inspection Checklist Verification 

Prior to a scale test, all items on the Inspection Checklist must be evaluated for consistency with 

conditions at calibration. All fluids must be at the levels recorded at the time of calibration and 

all tires must be in good condition. 
NIST Handbook 105-8 October 2003 16

9.5 Weight Cart Cleanliness 

The weight cart shall be maintained free of all visible contamination; this includes but is not 

limited to: mud, lubricants, water or product being weighed. 

9.6 User Modifications 

User modifications of weight carts are discouraged. However, it is recognized that 

modifications, e.g., installation of warning beacons, may be required. Such modifications 

performed by or at the request of weight cart users must be permanent changes to the weight 

cart, and become a fixed part of the weight cart structure. Items that are part of such 

modifications and which may be easily removed must be permanently attached to the weight cart 

using wire seals or tamper indicating materials, as required in section 6.4. Modifications must be 

documented in the maintenance log as required in section 9.3 and include a list of materials and 

drawings that detail the modification. The weight cart shall be recalibrated and adjusted to the 

nominal empty weight specified on the manufacturer’s identification plate upon completion of 

any modifications. If adjustment to the original nominal empty weight is not feasible, the weight 

cart should be adjusted to the lowest possible nominal empty weight from paragraph 4.1.1 and a 

new identification plate procured that reflects the new nominal empty weight. 

9.7 Licensing of Weight Cart Operators (Informational) 

According to the U.S. Department of Labor, Occupational Safety and Health Administration 

(OSHA) web page, a weight cart may be considered to be a Powered Industrial Truck. Owning 

organizations and operators should contact the office of OSHA responsible for their operational 

area for a written determination of the weight cart status. More information can be obtained 

from: OSHA, Directorate of Safety Standards Programs; U.S. DEPARTMENT OF LABOR; 

Room N3621; 200 Constitution Avenue, N.W; Washington, D.C. 20210. Telephone (202) 693-

2082; FAX (202) 693-1663. If the weight cart is designated a Powered Industrial Truck, the 

operator must complete an operator training course, and a daily safety inspection and checklist 

are required. A sample checklist is provided as Attachment 2. Use of a similar checklist is 

suggested for all weight carts, regardless of OSHA status, to assist in maintaining good 

maintenance records. 
NIST Handbook 105-8 October 2003 17

 Figure 1 

Typical Liquid Fuel Powered Weight Cart Configurations 

Typical configurations of a liquid fueled weight cart with up to 6 000 lb net weight and 

up to 37 500 lb gross weight. 

Note: Cart dimensions vary 

according to weight size and 

customer needs. 
NIST Handbook 105-8 October 2003 18

Figure 2 

Typical Electrically Powered Weight Cart Configurations 

Typical configurations of electrically (battery) powered weight carts with up to 4 000 lb 

net weight and up to 20 000 lb gross weight.
NIST Handbook 105-8 October 2003 19

Attachment 1 

Example Fuel Tank Drawing 

Scale plate 

markings shown 

for example 

only. 

Other formats 

are acceptable

Safety Cap 

Thread for fuel outlet 

fitting. Other fitting 

locations permitted.
NIST Handbook 105-8 October 2003 20

Attachment 2 

Example Daily Weight Cart Inspection Checklist

(Must be altered to fit the weight cart in use) 

Weight cart identification number 

Weight cart manufacturer 

Weight cart model number 

Weight cart serial number 

Walk Around 

(OK) 

 (Inspection starts at operator platform) Needs 

Attention 

Date 

Corrected

1. No evidence of metal fatigue on cart structure (e.g. cracks) 

2. No evidence of fluid leaks 

3. Tire Integrity (e.g. major nicks, cracks, cuts contamination) 

4. Wheels secured 

5. Major components secured in place (e.g. Engine, battery, 

fuel tank, hydraulic pump) 

 

6. Engine oil level correct and oil not grossly contaminated 

7. Hydraulic oil level correct and oil not grossly contaminated 

8. Operator platform level and securely attached 

9. All guards and shields in place and secure 

10. Steering components securely attached 

11. All tamper indicators in place 

12. Fuel tank filled to proper level 

13. All labels and decals in place 

 

Operational Checklist

(OK) 

 (Start weight cart motor and test controls) Needs 

Attention 

Date 

Corrected

1. Engine starts and operates properly 

2. Steering mechanism works properly 

3. No fluid leaks 

4. Forward/reverse controls functioning properly 

5. Warning beacons functional (if equipped) 

6. Rail gear functional (if equipped)