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SOP 33

Standard Operating Procedure

for

Calibration of Weight Carts

1 Introduction

This Standard Operation Procedure (SOP) describes the procedure to be 

followed for the calibration of weight carts used to test livestock and vehicle 

scales. This procedure may be used for any nominal values provided 

adequate standards and equipment are available and the item being 

calibrated meets appropriate specifications. Detailed measurement ranges, 

standards, equipment, and uncertainties for this SOP are generally compiled 

in a separate document in the laboratory.

Prerequisites

Facility. Verify that the laboratory facilities meet the following 

minimum conditions to meet the expected uncertainty possible with 

this procedure.

Table 1. Environmental conditions.

Echelon Temperature Requirements During a Calibration Relative Humidity

(%)

III Lower and upper Limit: 18 °C to 27 °C

Maximum changes: ± 5 °C / 12 h and ± 3 °C / h 40 to 60 ± 20 / 4 h

Balance/scale. Verify that the balance, scale, or load cell is in good 

operating condition with sufficiently small process standard 

deviation as verified by a valid control chart or preliminary 

experiments to ascertain its performance quality. The expanded 

uncertainty (k = 2) must be less than one-third of the applicable 

tolerance and balance operating characteristics must be evaluated 

against this requirement prior to calibration. 

If a scale or load cell is used for the calibration that is not a 

permanent piece of equipment in the calibration laboratory, 

appropriate verification and repeatability statistics must be obtained 

prior to a calibration to determine suitability and acceptability for 

calibration. Records must be maintained of this verification. 

Minimum verification includes an increasing and decreasing load 

test to at least the capacity of the weight cart, a shift test, a sensitivity 

test at the test load, and evaluation of the repeatability based on a 

minimum of 7 repeated weighings (following the same SOP to be 

used to test the weight cart). 
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Standards. Ensure the availability of suitable working standards or 

recently calibrated (and unused) field standards in quantities up to 

the capacity of the weight cart(s) that will be calibrated. All 

standards must have known conventional mass values with valid 

metrological traceability to the SI, which may be through laboratory 

working standards to the National Institute of Standards and 

Technology.

Standards must be evaluated to ensure that standard uncertainties for 

the intended level of calibration are sufficiently small. Reference 

standards should not be used to routinely calibrate customer 

standards using this procedure. The expanded uncertainty (k = 2) 

must be less than one-third of the applicable tolerance and evaluated 

prior to calibration. The contribution of the mass standards must be 

assessed prior to calibration and Class F mass standards without 

corrections or with uncertainties greater than 1/3 of the tolerance 

will not be acceptable.

Staff. Verify that the operator is experienced in precision weighing 

techniques and has had specific training in SOP 8, SOP 4, SOP 29, 

and GMP 10. Safety precaution: weight carts should be calibrated 

with at least two people present.

2 Methodology

Scope, Precision, Accuracy

This method is applicable to lower echelon mass calibration (tolerance 

testing) of weight carts, provided that the uncertainty requirements can be 

met. The achievable precision using this procedure is appropriate, provided 

the expanded uncertainty of the measurement is no more than one-third of 

the permissible tolerance of the weight cart. The accuracy achievable with 

this procedure depends on the accuracy of the calibration of the working 

standards and the precision of the comparison equipment/devices chosen 

and the procedure selected (e.g., SOP 8 or SOP 4).

Summary

A weight cart is calibrated by substitution with standards having known 

values, using weighing equipment that has been evaluated as having 

sufficient resolution and repeatability, to maintain uncertainty to tolerance 

ratios needed in legal metrology. Modified or double substitution methods 

are used (SOP 8, SOP 4) and are modified to obtain the replicate 

observations needed for measurement assurance and determination of the 

calibration uncertainty. 
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Equipment /Apparatus/Assistance

A balance, scale, or load cell with suitable resolution and 

repeatability, in good repair.

2.3.1.1 General guidelines regarding selection of weighing 

equipment must include consideration of the device 

repeatability to determine the achievable standard deviation 

of the measurement process. To ensure that appropriate 

uncertainty to tolerance ratios are maintained, the following 

guidance is provided: 

When using Modified SOP 8: 

− For a 1000 lb to 2000 lb cart, the maximum division size 

should be 0.01 lb or less.

− For a 5000 lb cart, the maximum division size should be 

0.05 lb or less.

When using Modified SOP 4: 

− For a 1000 lb to 2000 lb cart, the maximum division size 

should be 0.05 lb or less.

− For a 5000 lb cart, the maximum division size should be 

0.1 lb or less.

Some balances will require suitable supports to be mounted 

on the scale deck (platform) to receive the weight cart 

dimensions without damage to the scale or weight cart. 

Supports must be appropriately stable and sturdy. 

Standards and correction weights, meeting NIST Class F tolerances 

with current Calibration Reports and known values and uncertainties 

(as listed with prerequisites).

Hand tools such as the following are needed: wrenches; screw 

driver; wire cutters; lead and wire seals, and seal press. 

Means to move the weight cart safely. Weight carts are large, bulky 

items and are awkward to move safely. Appropriate safety 

precautions must be followed in the laboratory. Movement of liquid 

powered fuel carts is usually not done using the power system of the 

carts because exhaust from gasoline or diesel powered carts is 

considered unsafe in the laboratory; if no other options exist, 

suitable air handling must be available. Use of forklifts to move the 

carts should only be considered when other options are unavailable 

and extreme care must be taken. Use of a hoist may provide adequate 

means to move the cart, however, adequate care must be taken to 

prevent tipping the cart or bumping into other items in the laboratory 

as the cart is lifted and moved.
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A basic knowledge of weight carts, including the braking system 

and operating controls is required. Only qualified personnel should 

operate and inspect the weight cart. Verification that the brakes are 

operative prior to movement of the cart is essential.

Suitable adjustment material must be available for placement in the 

adjusting compartments; lead or steel shot is recommended.

Inspection checklist (See Appendix A). Weight carts are not 

considered Class F standards due to the extent of motorized and 

mechanical parts and fluids; therefore, special care must be taken in 

their calibration and use. An inspection checklist must be completed 

for each new cart prior to placing it into service. The checklist 

becomes a permanent part of the records for each weight cart and 

must be available for review prior to each use or calibration.

For safety reasons, two people should be present to conduct a 

calibration of a weight cart.

3 Fundamental Considerations

Weight carts must be properly cleaned and painted, with all repairs and 

maintenance completed (as needed) prior to calibration. Obtaining actual 

“as found” values for reverse traceability is not possible with this procedure. 

Obtaining “as found” values may be achieved by performing a calibration 

before and after repairs and maintenance are completed. Alternatively, see 

the “Recommended Method for Intermediate Verification of Mass Values 

for Weight Cart Users” included as Appendix B.

Weight carts must be completely dry, with no ice or moisture on the surface 

or under carriage of the cart.

Experience has shown that a light coating of frost can cause errors more 

than the tolerance for the cart. In heated facilities, the cart must be allowed 

enough time to warm to prevent condensation.

Table 2. Stabilization Time.

Temperature Range

22 oC (lab temp)

Temperature Range

72 oF (lab temp)

Minimum

Equilibration Timea

± 5 oC, 17 oC to 28 oC ± 10 oF, 62 oF to 82 oF 4 hours

< 17 oC and > 28 oC < 62 oF and > 82 oF 24 hours/overnight

a

deviation is allowed if the known cart temperature is at the lab temperature ± 2.5 oC (5 oF).
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Weight carts that repeatedly demonstrate excessive “as found” out-oftolerance conditions from the previous calibration date, may be required to 

be submitted on a more frequent basis; with every consideration being given 

to determine the cause of the variance.

4 Pretest Weight Cart Inspection 

Complete the Weight Cart Inspection Checklist that is included in Appendix A. The 

Inspection Checklist is an integral part of the Calibration Report of a weight cart 

and must be transported with each weight cart and verified prior to each use or 

calibration. Note and ensure completion of any needed repairs or maintenance prior 

to calibration. 

5 Procedure

Follow SOP 8 or SOP 4 to determine the conventional mass value of the 

weight cart, except for items modified and clarified in this SOP. Follow 

good laboratory practices such as properly exercising the balance prior to 

calibration.

SOP 8 Modifications.

Repeat the intermediate weighing of the weight cart as if multiple 

weights were being verified. Obtain at least 3 observations that are 

taken with a release/removal of the weight from the sensing device. 

Determine the calculated differences per SOP 8 and calculate the 

range between the largest and smallest numerical mass value 

differences. Record the range values in a suitable control chart for 

weight cart calibrations.

Mass adjustments to the cart may be made at the end of exercising 

the balance or after the first observation. The cart must be adjusted 

as close as possible to zero error. The first reading then becomes a 

“zero” difference when compared to the standards (the correction 

values of the standard must be considered). Adjustments must be 

made quickly to avoid errors due to balance drift or shifting. If

balance drift or shifts are noticed, the 3 replicate observations should 

be made after the adjustment is completed.

Care must be taken to ensure that the center of the mass of the weight 

cart is centered on the balance pan as much as is possible. By 

rotating the cart by 180 degrees and remeasuring it, off-center 

loading factors may be considered as a part of standard deviation. 

SOP 4 Modifications.

Repeat the double substitution procedure 3 times. Determine the 

calculated differences per SOP 4 and calculate the range between 
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the largest and smallest differences. Record the range information 

in a suitable control chart for weight cart calibration range values.

Mass adjustments to the cart may be made at the end of exercising 

the balance or after the first double substitution. The cart must be 

adjusted as close as possible to zero error. The first reading then 

becomes a “zero” difference when compared to the standards (the 

correction values of the standard must be considered). Adjustments 

must be made quickly to avoid errors due to balance drift or shifting. 

If balance drift or shifts are noticed, the 3 replicate double 

substitutions should be made after the adjustment is completed.

Care must be taken to ensure that the center of the mass of the weight 

cart is centered on the balance pan as much as is possible. By 

rotating the cart by 180 degrees and remeasuring it, off-center 

loading factors may be considered as a part of standard deviation. 

6 Calculations

Follow calculations as described in SOP 4 or SOP 8 as appropriate.

Calculate and report the mean of the 3 replicate measurements as the 

calibrated mass of the weight cart. When adjustments are made, use the 

mean of the adjusted value as the “as left” reported value. 

7 Tolerance

Tolerances are established in NIST Handbook 105-81. Weight carts must be 

adjusted as close as possible to zero error during calibration. The expanded 

(k = 2) combined uncertainty of the calibration must be less than one-third 

of the tolerance specified in Handbook 105-8. 

The values of weight carts and their tolerance status are issued and 

evaluated based on Conventional Mass (previously called Apparent Mass 

versus a reference density of 8.0 g/cm3 at 20 °C). If a reference density other 

than 8.0 g/cm3 is used, the reference density must be reported. No correction 

for the effect of air buoyancy is general made unless stated on the test report.

 1 NIST Handbook 105-8, Specifications and Tolerances for Weight Carts, 2019.
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Tolerances for weight carts (See also NIST Handbook 105-8). Tolerances 

are calculated as 0.035 % of the nominal mass, rounded to the nearest 10

grams.

Table 3: Weight Cart Tolerances

Nominal 

(lb)

Tolerance 

(± g)

Nominal 

(kg)

Tolerance 

(± g)

Nominal 

(kg)

Tolerance 

(± g)

1000 160 400 140 2600 910

1500 240 500 170 2700 940

2000 320 600 210 2800 980

2500 400 700 240 2900 1010

3000 480 800 280 3000 1050

3500 560 900 310 3100 1080

4000 640 1000 350 3200 1120

4500 710 1100 380 3300 1150

5000 790 1200 420 3400 1190

5500 870 1300 450 3500 1220

6000 950 1400 490 3600 1260

6500 1030 1500 520 3700 1290

7000 1110 1600 560 3800 1330

7500 1190 1700 590 3900 1360

8000 1270 1800 630 4000 1400

8500 1350 1900 660 4100 1430

9000 1430 2000 700 4200 1470

9500 1510 2100 730 4300 1500

10000 1590 2200 770 4400 1540

2300 800 4500 1570

2400 840 4600 1610

2500 870

8 Measurement Assurance

Adequate measurement assurance is a required component of every quality 

system and uncertainty analysis but maintaining a surrogate weight cart for 

use in the laboratory as a check standard is impractical.

Three repeated observations are made and the standard deviation of the 

values or the range of values (largest mass difference minus the smallest 

mass difference) is entered in a control chart. The pooled standard deviation 

of the process is used, or the pooled mean range value is used to estimate a 

standard deviation of the process. When plotting each new variability value, 

verify that it is within previously accepted limits. 

Alternatively, though not preferred, 7 to 12 repeated observations are made 

(following the same SOP to be used to test the weight cart) and a short-term 
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standard deviation of the process is calculated each time a weight cart is 

calibrated. A minimum of 7 replicate weighings may be used if a balance is 

not permanent equipment of the laboratory (with additional balance 

evaluations). 

9 Assignment of Uncertainty 

The limits of expanded uncertainty, U, include estimates of the standard uncertainty 

of the mass standards used, us, and estimates of the standard deviation of the 

measurement process, sp. These estimates should be combined using the root-sumsquared method (RSS), and the expanded uncertainty, U, reported with a coverage 

factor of two (k = 2), to give an approximate 95 percent level of confidence. See 

SOP 4 or SOP 8 for a detailed uncertainty budget table as appropriate. See SOP 29 

for the complete standard operating procedure for calculating and reporting the 

measurement uncertainty. 

The expanded uncertainty for the standards, U, are obtained from the 

calibration report. The combined standard uncertainty, uc, is used and not 

the expanded uncertainty, U, therefore the reported uncertainty for the 

standards will usually need to be divided by the coverage factor k.

A combination or summation of standards is typically needed for the 

calibration of weight carts. The dependence or independence of the 

calibration of such standards must be determined prior to combining 

the uncertainties associated with the standards. In the case of 

dependent standards (calibrated against the same working standard), 

the us values are summed by addition prior to including them in a 

root sum square calculation: (us1 + us2 + ... usn). In the case of 

independent standards, the us values are summed by root sum 

square: (us1

2 + us22 +...usn2

)

0.5. All us values must represent one 

standard deviation prior to combining.

Standard deviation of the measurement process, sp, is obtained by using the 

pooled standard deviation of similar size carts over time or by calculating 

the estimated standard deviation of the process based on the mean range 

value calculated from applicable range charts

Buoyancy corrections are not generally needed at the uncertainty level this 

procedure is designed for. An uncorrected systematic error should be 

included for the uncorrected magnitude of the air buoyancy correction, 

following NISTIR 6969, SOP 2; this value is treated as a rectangular 

distribution. 

Additional components due to balance drift or sensitivity errors need to be 

evaluated and may need to be included per SOP 8. 
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10 Calibration Certificate

Prepare a Calibration Certificate according to SOP 1. Report the mean of 

the calculated conventional mass measurement result and the calculated 

uncertainty. A sample calibration certificate is included in Appendix A; 

review the final certificate against the checklist provided in SOP 1. 

Conformity Assessment.

The Inspection Checklist is an integral part of the calibration certificate. The 

expanded uncertainty, U, must be ≤ 1/3 of the applicable tolerance from 

NIST Handbook 105-8. Compliance assessments must note the applicable 

documentary standard and which portions of the standard were or were not 

evaluated.
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Appendix A

Sample Calibration Certificate

for

Weight Cart 

Test Number: Date Issued: Date of Calibration: 

Submitted by: 

Manufacturer: Date of Manufacture: 

 

Model Number: Identification/Serial Number: 

Calibration Values:

As Found

Conventional Massa (lb)

As Left

Conventional Mass (lb) Uncertainty (lb)

a The Conventional Mass is the mass determined/calculated by weighing in air of reference density 

1.2 mg/cm3

, reference weights of density 8.0 g/cm3 and at a reference temperature of 20 °C. 

Buoyancy corrections are considered negligible and were not made unless otherwise stated. 

Conditions of Test & Traceability:

The above weight cart was compared with standards of the State of XXXX, which are 

traceable to the International System of Units (SI) and/or the National Institute of Standards 

and Technology (NIST) and have current calibration values. The assigned test number 

shown above provides documented evidence for metrological traceability. 

Test method: {Enter SOP 4 or 8 as applicable} NISTIR 6969, Selected Procedures for Mass 

Calibrations. {Enter publication date} 

Balance:

Temperature:

Pressure:

Relative Humidity:

Components of Uncertainty:

The uncertainty is reported as an expanded uncertainty at an approximate 95 % confidence 

interval (k = 2) and calculated according to SOP 29 which is compliant with the ISO/IEC

Guide to the Expression of Uncertainty in Measurement. Components included in the 

calibration uncertainty are the uncertainty associated with the standards and the standard 

deviation of the measurement process as determined through repeated observations or other 

suitable range chart for this measurement process. Factors included on the inspection 

checklist have not been included in the calibration uncertainty. However, factors on the 
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checklist may contribute measurement errors that are significant if not properly maintained 

during use.

Conformity Assessment:

The weight cart identified on this calibration certificate complies with NIST Handbook 

105-8, 2019 specifications and tolerances. Additional details regarding the assessment are 

included in the associated checklist that is an integral part of this calibration certificate. 

The weight cart was found (or adjusted) to within the specified tolerances.
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Inspection Checklist

The weight cart was cleaned and painted and allowed to come to thermal and environmental 

equilibrium in the laboratory prior to calibration. The weight cart was adjusted (as needed 

and noted above) as close as possible to zero error. All fluid levels were adjusted as close 

as possible to the full/reference marks and sealed. Liquid levels must be maintained as 

close to reference levels as possible during use. The fluid levels include:

_____Engine Oil;

_____Hydraulic Fluid (sealed); 

_____Battery Water Level (sealed battery); and 

_____Liquid Fuel {Enter gasoline or diesel here} (note reference mark). 

The attached Inspection Checklist is an integral component of this Calibration Report and 

a copy must be maintained with the cart and reviewed prior to use.

Any maintenance, repairs, replacement of parts, or damage to weight cart or its components 

will likely result in an out-of-tolerance condition; therefore, maintenance or replacement 

of components such as batteries, tires, filters, or other items listed on the checklist, require

calibration of the weight cart prior to subsequent use. 

Tolerance: 

Reference: NIST Handbook 105-8, Specifications and Tolerances for Weight Carts, 2019. 

The applicable tolerances are as follows: 

Inspection Checklist Table 1: Weight Cart Tolerances

Nominal 

(lb)

Tolerance 

(± g)

Nominal 

(kg)

Tolerance 

(± g)

1000 160 500 170

2000 320 1000 350

3000 480 1500 520

4000 640 2000 700

5000 790 2500 870

6000 950 3000 1050

7000 1110 3500 1220

8000 1270 4000 1400

9000 1430 4500 1570

10000 1590

For carts intermediate between these values, tolerances are calculated as 0.035 % of the nominal 

mass, rounded to the nearest ten grams.

Authorized Signature
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Inspection Checklist for Weight Cart

Test Number: Date of Inspection: 

Manufacturer: Date of Manufacture: 

 

Model Number: ID/SN Number: 

_____Nominal Mass of Weight Cart: __________ Suitably marked: Yes/No

_____Powered by: Electric/Generator__________ Diesel__________ Gasoline 

__________

_____Fluid Levels: Engine Oil __________ 

Hydraulic Fluid __________ Sealed: Yes/No

Battery __________ Sealed: Yes/No

Liquid Fuel __________ Reference line present: Yes/No

_____Fluid drain tubes extend beyond the body of the cart: Yes/No

_____Number of axles: __________

_____Number/Size of Tires: __________

_____Sealed wheel bearings: Yes/No

_____Drain holes present in locations where water may accumulate: Yes/No

_____Weight restraint railing permanently fixed and solid: Yes/No

_____Adjusting cavity accessible: Yes/No

_____Adjusting cavity approximate capacity: ______lb

_____Adjusting cavity sealed: Yes/No 

_____Service brakes functioning properly: Yes/No 

_____Parking brakes functioning properly: Yes/No

_____Remote control functioning properly: Yes/No

_____General condition at time of calibration (note any accumulated dirt/debris, damage, 

loose parts, or evidence of tampering or unauthorized entry of seals).

_____List and report any repair and maintenance performed, parts replaced, etc., Leaks 

repaired, new battery, carburetor, exhaust system, wheels changed, welding performed, 

etc. Include any comments or changes since the last calibration.
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Appendix B

Recommended Method 

for 

Intermediate Verification of Mass Values 

for Weight Cart Users

1. Introduction

1.1. This Recommended Method is intended to provide an intermediate 

verification of weight cart mass values to obtain a rough estimate of an “as 

found” value to provide adequate evidence for or against the need for 

corrective action on scales that have been tested. 

1.2. This method may be performed as often as needed during a calibration cycle 

as a preventive action due to the inherent instability of weight cart mass 

values. It should also be performed prior to repairs or maintenance to obtain 

and record adequate evidence of mass values and calibration status prior to 

the change of mass values resulting from repair and maintenance. 

1.3. Records of all such intermediate tests should be retained with the Inspection 

Checklist and should be submitted with the completed Inspection Checklist 

when the weight cart is submitted for calibration.

1.4. This method may NOT be used as a substitute for a proper laboratory 

calibration according to SOP 33 and does NOT provide a traceable mass 

value with an appropriate calibration uncertainty. Recall that the error on 

the standard must be less than one third of the applicable tolerance applied 

to a scale under test. This level of verification is difficult and may be 

impossible to determine under field conditions. Only errors more than

Handbook 44 requirements may be determined using this method.

2. Prerequisites

2.1. Facility. Intermediate verification tests are normally conducted under field 

or under maintenance shop/garage conditions rather than in a controlled 

laboratory environment. As such, the avoidance of extreme conditions of 

temperature, wind, and precipitation are critical. A rough estimate of 

conditions at the time of verification must be recorded when data is 

obtained. 

2.2. Equipment. A suitable scale must be selected. This typically needs to be of 

better resolution than the scales being tested with the weight cart or as a 

minimum, a scale with the smallest resolution on which the cart may be 

used. A repeatability test, with a minimum of 3 repetitions is needed to 

ensure that the mass values will repeat to within one-half of a scale division 

at the load of the weight cart. 
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2.3. Standards. Class F field standards are used if they are within the prescribed 

calibration cycle. A small Class F weight kit is used as correction weights 

to determine small errors and partial division values.

2.4. Staff. Staff must be trained in substitution calibration methods and be able 

to perform calculations associated with determining mass values. 

2.5. The weight cart fuel levels, where liquid fuels are used, must be set at the 

reference mark on the fuel sight gauge.

3. Fundamental Considerations

Weight carts must be completely clean and dry, with no mud, ice or moisture on 

the surface or under carriage of the cart. Tires must be cleaned as well. (Values 

obtained under actual operating conditions may provide some insight to the user 

regarding the impact of maintenance and cleanliness of the weight cart). 

4. Pretest Weight Cart Inspection 

Complete the Weight Cart Inspection Checklist that is included in Appendix A. 

5. Procedure

5.1. Establish scale repeatability with a minimum of three repetitions such that 

the scale repeats to within one-half of a division at the weight cart capacity.

5.2. Load Class F field standards onto the scale in the same location(s) where 

the weight cart will be placed to the same load as the stated conventional 

mass of the weight cart. Assign a mass value to this summation of standards 

based on the nominal values of the weights. The added mass values of these 

weights is the value for your standards. With the weights loaded on the scale 

deck, use small error weights to determine the break point of the nearest 

larger scale division. 

5.3. Remove the large Class F field standards and leave the small error weights 

on the scale.

5.4. Load the weight cart onto the scale in the same location(s) where the 

weights were loaded. Add or remove the small error weights until the scale 

responds in the same way as the previously loaded mass standards to 

determine the break point of the same scale division. 

6. Calculations

Calculate the difference between the error weights used with the Class F field 

standards and the error weights used with the weight cart. Because this is not an 

accepted calibration method, the observed difference in these values only represents 

an estimated mass value. (Error weights used with Class F standards – Error 

weights used with the weight cart = Observed Estimated Error).
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7. Tolerance and Evaluation

The observed estimated error must be less than one third of the smallest tolerance 

applied to a scale on which the weight cart might be used. Corrective action is 

required if the observed mass of the weight cart exceeds the calibrated mass by 

more than one-third of the applicable tolerance.

8. Measurement Assurance

Measurement assurance is obtained through three replicate measurements. 

9. Assignment of Uncertainty 

An uncertainty is not calculated, estimated, or assigned with this intermediate 

verification method. It is not considered a valid calibration with evidence of 

traceability. 

10. Calibration Certificate

A calibration certificate is not prepared for an intermediate verification. Recorded 

and observed data must be maintained. 
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Example of Intermediate Verification Procedure and Calculations

A. A 2000 lb weight cart is to be tested on a scale with 10 lb divisions.

B. When 2) 1000 lb Class F field standards are placed on the scale, the scale reading 

repeats to within one-half of a division when 3 replicate weighings are performed 

(weights must be moved on and off the scale or the scale arrested and released to 

determine this repeatability). The scale reads 2000 lb for each test.

C. Error weights are slowly placed on the scale deck in increments of 0.1 lb and the 

addition of 5.5 lb causes the scale to read the next larger division of 2010 lb.

D. The 2) 1000 lb Class F field standards are removed and the 2000 lb weight cart is 

placed on the scale deck, leaving the previous 5.5 lb error weights. Error weights 

of 6.5 lb are needed for the scale to break to 2010 lb with the weight cart on the 

scale deck (an additional 1.0 lb was added).

E. Error weights used with Class F standards = 5.5 lb

F. Error weights used with the weight cart = 6.5 lb.

G. Error weights used with Class F standards – Error weights used with the weight 

cart = Observed Estimated Error; 5.5 lb – 6.5 lb = - 1 lb

H. Evaluation: the smallest tolerance on the scale will be one-half of a division, or 

5 lb. One third of 5 lb is 1.7 lb. The error on standards used on the scale must be 

less than this level. The observed error on the cart of – 1.0 lb is less than 1.7 lb 

and corrective action for previous scale tests is not needed at this time. The - 1 lb 

value is recorded on the Inspection Checklist as an Intermediate Verification.

I. If the cart has been damaged or if repairs to the cart are needed, calibration is 

required at this time.
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