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SOP 7 

Recommended Standard Operating Procedure

for

Weighing by Single Substitution

Using a Single-Pan Mechanical Balance, a Full Electronic Balance, or a

Balance with Digital Indications and Built-In Weights

1 Introduction

Purpose

In the single substitution procedure, a standard and an unknown weight of equal 

nominal value are compared once to determine the difference in weights. Errors in 

any built-in weights or in the balance indications are minimized by using the 

balance only as a comparator and by calibrating the balance indications over the 

range of use for the measurement with a sensitivity weight. This procedure is 

suitable for calibration when moderate accuracy (OIML1 Classes F1 to M3, ASTM2

Classes 3 through 7) is required and as a single substitution, does not eliminate 

errors due to drift. The procedure incorporates measurement assurance through 

replicate tests using a check standard to monitor the reference value(s) of the 

standard and the repeatability of the measurement process over time. This 

procedure may be used for any nominal values provided adequate standards and 

equipment are available. Detailed measurement ranges, standards, equipment, and 

uncertainties for this SOP are generally compiled in a separate document in the 

laboratory.

Prerequisites 

Valid calibration certificates with appropriate values and uncertainties must 

be available for all reference standards used in the calibration. All standards 

must have demonstrated metrological traceability to the international 

system of units (SI), which may be to the SI through a National Metrology 

Institute such as NIST.

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. 

Verify that the balance that is used 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 when 

a new balance is put into service. 

 1 OIML is the International Organization for Legal Metrology. Weight classes are published in OIML R 111, which 

is freely available at http://www.oiml.org.

2 ASTM International (formerly the American Society for Testing and Materials) publishes the E617 standard for 

mass specifications and tolerances.
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Verify that the operator is experienced in precision weighing techniques and 

has had specific training in SOP 2, SOP 7, SOP 29, GMP 4, and GMP 10. 

Laboratory facilities must comply with the following minimum conditions 

to meet the expected uncertainty possible with this procedure and to comply 

with the balance manufacturer’s operating conditions specified for the 

balance. The laboratory environment must be stable within the stated limits 

for a minimum of 24 hours before a calibration.

Table 1. Environmental conditions.

Echelon3 Temperature Requirements During a Calibration Relative Humidity

(%)

II Lower and upper limits: 18 °C to 23 °C

Maximum changes: ± 2 °C / 12 h and ± 1.5 °C / h 40 to 60 ± 10 / 4 h

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

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

It is important that the difference in temperature between the weights and 

the air in the laboratory or inside the mass comparator be less than the values 

noted in the Procedure section. Standards and test artifacts must be allowed 

to reach equilibration in or near the balance before starting measurements.

2 Methodology

Scope, Precision, Accuracy

This method is applicable to all weighings utilizing a single-pan mechanical 

balance, a full electronic balance, or a balance that combines digital indications 

with the use of built-in weights (combination balance). The precision depends upon 

the sensitivity of the balance and the care exercised in making the required 

weighings. The accuracy achievable with this procedure depends on the accuracy 

of the calibration of the working standards and the precision of the intercomparison. 

Summary

The balance is adjusted, if necessary, to obtain balance indications for all 

measurements that will be within the range of the optical scale or digital indications 

of the balance without changing the dial settings for the built-in weights, if present. 

The standard and the test weight are each weighed. A small, calibrated weight, 

called a sensitivity weight, is added to the test weight and these are weighed 

The single substitution procedure is the same for all the balances mentioned above,

but the adjustment of the balance to prepare for the intercomparison and the 

selection of the sensitivity weight differ slightly depending upon the balance used. 

 3 Echelon II corresponds to weights of Classes OIML F1 and F2, ASTM Classes 2, 3 and 4. Echelon III corresponds 

to weights of Classes OIML M1, M2, and M3, ASTM Classes 5, 6 and 7. This procedure does not provide adequate 

redundancy for OIML Classes E1 or E2, ASTM Classes 000, 00, 0, or 1 and SOP 5 or SOP 28 should be used.
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When steps specific to a particular balance are required, they are given in 

subsections of the procedure identified by a, b, and c along with the balance type. 

Apparatus/Equipment Required

Precision analytical balance or mass comparator with sufficient capacity 

and resolution for the calibrations planned.

Calibrated working standards, of nominally equal mass to the unknown 

mass standards being calibrated. Calibrated tare weights are used as needed 

to ensure that the standard(s) and test artifacts are of equal nominal mass 

(See SOP 34 for suitable limits).

Calibrated sensitivity weights and tare weights selected to comply with the 

guidelines in SOP 34.

Uncalibrated weights to be used to adjust the balance to the desired reading 

range if needed.

Forceps to handle the weights, or gloves to be worn if the weights are moved 

by hand. Forceps and gloves must be selected to avoid damage or 

contamination of mass standards.

Stop watch or other timing device to observe the time of each measurement 

(calibration not required; this is used to ensure consistent timing of the 

measurement). If an electronic balance is used that has a means for 

indicating a stable reading, the operator may continue to time readings to 

ensure consistent timing that can minimize errors due to linear drift.

Calibrated barometer with sufficiently small resolution, stability, and 

uncertainty (See SOP 2, e.g., accurate to ± 66.5 Pa (0.5 mmHg)) to 

determine barometric pressure.4

Calibrated thermometer with sufficiently small resolution, stability, and 

uncertainty (see SOP 2, e.g., accurate to ± 0.10 °C) to determine air 

temperature.4

Calibrated hygrometer with sufficiently small resolution, stability, and 

uncertainty (see SOP 2, e.g., accurate to ± 10 percent) to determine relative

humidity.4

 4

The barometer, thermometer, and hygrometer are used to determine the air density at the time of the measurement. 

The air density is used to make an air buoyancy correction. The limits specified are recommended for high precision 

calibration.
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Symbols

Table 2. Symbols used in this procedure.

Symbol Description

S standard weight

X weight calibrated

Sc check standard

t small calibrated tare weight, A subscript s or x is used to indicate the weight(s) with 

which it is associated

sw small calibrated weight used to evaluate the sensitivity of the balance

M the mass (true mass) of a specific weight. Subscripts s, x, t, sw are used to identify 

the weight (equals Nominal plus Correction)

N the nominal value of a specific weight. Subscripts s, x, are used to identify the 

weight.

C the correction for a specific weight. Subscripts s, x, are used to identify the weight.

CM the conventional mass of a specific weight. Subscripts s, x, t, sw are used to identify 

the weight.

ρa density of air at time of calibration

ρn density of normal air (1.2 kg/m3

)

ρ density of masses; subscripts s, x, ts, tx, sw are used to identify the weight

Procedure

Preliminary Procedure

2.5.1.1 Weights are visually inspected for cleanliness and damage. 

2.5.1.2 If cleaning weights, it is important to clean weights before any 

measurements are made because the cleaning process may change 

the mass of the weight. Cleaning should not remove any significant 

amounts of weight material. Weights should be handled and stored 

in such a way that they stay clean. Before calibration, dust and any 

foreign particles shall be removed. Care must be taken not to change 

the surface properties of the weight (i.e., by scratching the weight). 

If a weight contains significant amounts of dirt that cannot be 

removed by the methods cited above, the weight or some part of it 

can be washed with clean alcohol, distilled water or other solvents. 

Weights with internal cavities should normally not be immersed in 

the solvent to avoid the possibility that the fluid will penetrate the 

opening. If there is a need to monitor the stability of a weight in use, 

the mass of the weight should, if possible, be determined before 

cleaning.

2.5.1.3 If weights are cleaned with solvents, they must be stabilized for the 

times given in the following table (better class weights need to 

stabilize for 7 to 10 days):
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Table 3. Cleaning stabilization.

Weight class F1 F2 to M3

After cleaning with alcohol 1 to 2 days 1 hour

After cleaning with distilled water 1 day 1 hour

2.5.1.4 Prior to performing any calibration tests, the weights need to be 

acclimated to the ambient conditions of the laboratory. In particular, 

weights of classes F1 (or better) should be close to the temperature 

in the weighing area and equilibrate for a minimum of 24 hours. The 

minimum times (in hours) required for temperature stabilization 

(depending on weight size, weight class and on the difference 

between the initial temperature of the weights and the room 

temperature in the laboratory) are shown in the table below (with 

appropriate documented evidence). As a practical guideline, a 

waiting time of 24 hours is recommended. If weights are extremely 

hot or frozen, additional equilibration may be needed to address 

problems with condensation and frozen surfaces. Weights must be 

completely dry prior to calibration.

Table 4. Minimum equilibration times. 5

ΔTa Nominal Mass OIML Class F1

(time in h)

OIML Class F2 to M3

(time in h)

± 20 °C

1 000, 2 000, 5 000 kg 79 5

100, 200, 500 kg 33 4

10, 20, 50 kg 12 3

1, 2, 5 kg 6 2

100, 200, 500 g 3 1

10, 20, 50 g 1 1

< 10 g 1 0.5

± 5 °C

1 000, 2 000, 5 000 kg 24 1

100, 200, 500 kg 10 1

10, 20, 50 kg 4 1

1, 2, 5 kg 3 1

100, 200, 500 g 2 1

< 100 g 1 1

± 2 °C <100 g to 5 000 kg 1 0.5

± 0.5 °C <100 g to 5 000 kg 0.5 0.5 a

ΔT = Initial difference between weight temperature and laboratory temperature.

 5 Consider equivalent ASTM Classes for equilibration times.
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2.5.1.5 Conduct preliminary measurements to obtain an approximate value 

for the difference between the standard and the unknown, to identify 

where in the weighing instrument range the readings occur, to 

determine if tare weights are required, to determine the sensitivity 

weight to be used, and to determine the time interval required for the 

weighing instrument indication to stabilize. See NISTIR 6969, SOP 

34 for specific instructions on evaluation of the need for and 

selection of tare weights and sensitivity weights. 

Tare weights are rarely needed for mass standards that are within 

applicable tolerances. When unequal nominal weights are 

compared, tare weights are often required. When tare weights are 

required, carry tare weights, ts and tx, with the standard and the 

unknown, S and X, respectively. The tare weights must be calibrated 

standards with valid uncertainties that are included in the process of 

determining mass values and calibration uncertainties. The standard 

and its tare weight, S + ts, should be "nearly the same mass" as the 

unknown with its tare weight, X + tx. "Nearly the same mass" 

depends upon the balance used (See SOP 34, Table 1). 

A sensitivity weight must be used on equal-arm balances, single-pan 

mechanical, and is usually used on electronic balances, to ensure 

that the measured differences between the standard(s) and unknown 

test items have valid accuracy and traceability (See SOP 34, Table 

2) (e.g., the optical/digital scale is calibrated each time the 

procedure is performed through the use of a sensitivity weight). 

If the sensitivity of the balance has been analyzed and is periodically 

evaluated and found to introduce negligible errors or uncertainties 

according to SOP 34 and measurement requirements, the equations 

in Section 3 must be modified to eliminate the sensitivity factor to 

avoid “division by zero” errors in the calculations. 

If a sensitivity weight will be used, select one that meets the criteria 

in SOP 34.

2.5.1.6 Determine whether optional sequence A or B will be used. Optional 

sequence A uses the standard on the balance for the first observation 

and the unknown on the balance for the second and third 

observations; this is often called the “SXX” sequence. Optional 

sequence B starts with the unknown on the balance first and with the 

standard on the balance for the second and third observations; this 

is often called the “XSS” sequence. 
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2.5.1.7 Adjust the single pan balance or the combination balance so the first 

two readings of the single substitution fall in the first quarter of the 

optical scale or digital indications. The zero adjustment and tare 

adjustment may be used. Small weights may be placed on the 

balance pan to reach the desired reading range. These weights 

remain on the pan throughout the single substitution. Once the 

balance has been adjusted to the desired position, neither the balance 

dials, the zero and tare adjustments, nor the small weights placed on 

the balance pan are to be changed during the measurement. 

2.5.1.8 If the balance is equipped with a pan arrestment mechanism, arrest 

the pan between each observation.

Measurement Procedure, Optional Sequence A (SXX) 

Table 5. Optional Sequence A.

Measurement No. Weights on Pan Observation

1 S + ts O1

2 X + tx O2

3 X + tx + sw O3

All observations should be recorded on suitable data sheets, such as those 

in the appendix. Record the laboratory ambient temperature, barometric 

pressure, and relative humidity.

2.5.2.1 Observation 1. Place the standard weight(s), S, along with ts on the 

balance pan. If equipped with a pan arrestment mechanism, release 

the balance pan. When the pan is released, start the stop-watch and 

record observation O1 once the balance indication has stabilized.

2.5.2.2 Observation 2. Remove weight(s) S and ts and replace with test 

weight X and its tare weight, tx. Release the pan, time the interval, 

and record observation O2.

2.5.2.3 Observation 3. Add the sensitivity weight, sw, to the weights of 

observation 2. Release the pan, time the interval, and record 

observation O3. 

2.5.2.4 If repeated single substitutions are performed, the values between 

successive trials should not differ from one another by more than ± 

2 sd of the balance. If this difference is exceeded, reject the data and 

take a new series of measurements that agree.

Measurement Procedure, Optional Sequence B (XSS)

Measurements for Option B are made as described in Option A except that 

X, S, tx, and ts are interchanged.
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Table 6. Optional Sequence B.

Measurement No. Weights on Pan Observation

1 X + tx O1

2 S + ts O2

3 S + ts + sw O3

3 Calculations

If no air buoyancy correction is performed, calculate the conventional mass 

correction, Cx, for the test weight as follows, according to the optional sequence 

used. Incorporate an uncorrected systematic uncertainty for the magnitude of the 

buoyancy correction in the uncertainty calculations according to SOP 2 if using this 

equation. In each case, the conventional mass corrections for the standard 

weight(s), Cs, the conventional mass of the tare weights, CMts and CMtx and the 

conventional mass of the sensitivity weight, CMsw, are included. The symbols Ns

and Nx refer to the nominal values of S and X, respectively. If nominal weights are 

equal and no tare weights are used, values for nominal values and tare weights may 

be entered as zero. 

Optional Sequence A (SXX)

( ) 2 1

3 2

() s x

sw

xs t t s x

CM C C CM CM O O N N

O O

 

=+ − + −   + −

  −  

Eqn. (1)

Optional Sequence B (XSS)

( ) 1 2

3 2

() s x

sw

xs t t s x

CM C C CM CM O O N N

O O

 

=+ − + −   + −

  −  

Eqn. (2)

Mass Calculation with Air Buoyancy Correction

Calculate the air density, ρa, as described in the Appendix to SOP No. 2, 

Option B.

Calculate the mass of the test weight, Mx, and its mass correction Cx using 

the mass of the standard weight(s), the tare weights and the sensitivity 

weights according to the optional sequence used.
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3.2.2.1 Optional Sequence A (SXX)

( ) 2 1

3 2

1

1 1 1 ( ) 

1

s X

S X

a

sw

aa a sw

St t

St t

X

a

X

M

M M M O O

O O

M

ρ

ρρ ρ ρ

ρρ ρ

ρ

ρ

        −             −+ − − − +−           −             =     −

 

Eqn. (3)

3.2.2.2 Optional Sequence B (XSS)

( ) 1 2

3 2

1 

1 1 1 ( ) 

1

S X

S X

a

sw

aa a sw

St t

St t

X

a

X

M

M M M OO

O O

M

ρ

ρρ ρ ρ

ρρ ρ

ρ

ρ

        −             −+ − − − +−             −           =     −

 

Eqn. (4)

Calculate the mass correction Cx, as follows:

CMN x xx = − Eqn. (5)

where Nx is the nominal value for X.

Calculate the conventional mass6 of X, CMx. It is recommended that the 

conventional mass and conventional mass correction be reported. Calculate 

the conventional mass correction using Eqn. 5 and be sure to designate 

differences between mass and conventional mass on the certificate.

x

n

n

1

1

8.0

x

x

M

CM

ρ

ρ

ρ

    −

  =     −  

Eqn. (6)

 6 Conventional Mass: “The conventional value of the result of weighing a body in air is equal to the mass of a 

standard, of conventionally chosen density, at a conventionally chosen temperature, which balances this body at this 

reference temperature in air of conventionally chosen density.” The conventions are: reference density 8.0 g/cm3

; 

reference temperature 20 °C; normal air density 0.0012 g/cm3

. Conventional mass was formerly called “Apparent 

Mass versus 8.0 g/cm3

” in the United States. See OIML D28 (2004).
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If requested, the apparent mass versus the reference density of brass may be 

calculated. This value should only be provided when requested by the 

customer for use when calibrating mechanical balances that have been 

adjusted to this reference density. (This is rare).

Apparent mass versus brass:

 

1

1

8.3909

n

x

x

x vs brass

n

M

AM

ρ

ρ

ρ

    −

  =     −  

Eqn. (7)

4 Measurement Assurance

Duplicate the process with a suitable check standard (See GLP 1, SOP 9, and SOP 

30).

Plot the check standard value on the control chart and verify that it is within 

established limits. 

All values must be entered in the control chart, unless a mistake (i.e., typographical 

error) is identified and corrected, to ensure the variability obtained for the process 

is not unduly reduced over time. The observed value of the check standard is 

compared to the accepted mean value of the check standard and divided by the 

standard deviation for the check standard observations over time. 

A t-test may be incorporated to check the observed value of the check standard 

against the accepted value using the following equation and a 95 % confidence 

level. The t-statistic is calculated for stability analysis. This equation monitors 

stability over time, but should not be used to assess for bias. A calculated t-value 

less than two is within the warning limits of the process. A calculated t-value 

between two and three represents a value between the warning limits and 

control/action limits. A calculated t-value exceeding three represents a value 

outside of the control/action limits and suitable action must be taken. Calculated 

values of the t-statistic may also be monitored over time to determine the presence 

of drift.

( )

p

c c

s

S S

t − = Eqn. (8)

Check standard measurement results obtained over time are used to calculate the 

standard deviation of the measurement process, sp.

The mean value of the check standard over time is also compared to an appropriate 

reference value of the check standard with respect to their applicable expanded 

uncertainties to evaluate bias and drift over time. The mean value over time may be 

used to monitor drift in the standard or check standard. Excessive drift or bias must 

be investigated and followed with suitable corrective action. See SOP 9, Section 

4.2 for assessment methodology. 
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Where SOP 9 is followed, and check standards are used for 2 to 3 nominal values 

per balance, more frequent calibration intervals may be needed to monitor the 

working standards and the larger standard deviation of the nominal values 

bracketing the nominal value should be used. If check standards were already 

checked on a given day and found to be in control, additional evaluations may be 

conducted, but are not required. 

5 Assignment of Uncertainty 

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

mass standards used, us, estimates of the standard deviation of the measurement process, 

sp, and estimates of the effect of other components associated with this procedure, uo. These 

estimates should be combined using the root-sum-squared method (RSS), and the expanded 

uncertainty, U, reported with a coverage factor of two (k = 2), to give us an approximate 

95 % level of confidence. See SOP 29 for the complete standard operating procedure for 

calculating the uncertainty. 

The expanded uncertainty for the standard, U, is obtained from the calibration 

certificate. The combined standard uncertainty, uc, is used and not the expanded 

uncertainty, U, therefore the reported uncertainty for the standard will usually be 

divided by the coverage factor k. Where the coverage factor or confidence interval 

is not given, the laboratory should either contact the calibration provider to obtain 

the correct divisor or use a value of k = 2, assuming that the expanded uncertainty 

was reported with an approximate 95 % confidence interval (95.45 %).

The value for sp is obtained from the control chart data for check standards using 

single substitution measurements. (See SOP No. 9.) Where the standard deviation 

of the measurement process from the control chart is less than the resolution of the 

balance being used, the laboratory may use the value of the balance division or may 

use the larger of the standard deviation of the process or the following estimate for 

repeatability is used to represent the standard deviation of the process:

0.6

3 p

d s d = ≈ Eqn. (12)

Include an uncorrected systematic standard uncertainty if no buoyancy correction 

was performed. Calculate the magnitude of the air buoyancy correction per SOP 2 

and use a rectangular distribution. The uncertainty associated with air density and 

its associated factors may be calculated using the formula options provided in SOP 

4 or 5.

Other standard uncertainties that may be included at this calibration level include 

standard uncertainties associated with the density of the standards used, and may 

include any noted bias that has been determined through analysis of control charts 

and round robin data. See SOP 2, 4, and 29 for additional details.

Example components to be considered for an uncertainty budget table are shown in 

the following table.
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Table 7. Example uncertainty budget table.

Uncertainty Component Description Symbol Source Typical Distribution

Uncertainty of the standard mass(es) (5.1) us Calibration certificate

Expanded uncertainty 

divided by coverage 

factor

Accepted standard deviation of the 

process (5.2) sp

Control chart, standard 

deviation chart

OR estimates when sp is 

smaller than balance 

division

Normal

Uncertainty of the air buoyancy 

correction (5.3) ub

SOP 2 or OIML R111

Or Options as given in 

SOP 4

Rectangular

Uncertainty associated with bias (5.4) ud

Control chart, proficiency 

tests See SOP 29

Draft a suitable uncertainty statement for the certificate. For example:

The uncertainty reported is the root sum square of the standard uncertainty of the 

standard, the standard deviation of the process, and the uncertainty associated with 

the buoyancy corrections, multiplied by a coverage factor of 2 (k = 2) for an 

approximate 95 percent confidence interval. Factors not considered in the 

evaluation: magnetism (weights are considered to meet magnetism specifications 

unless measurement aberrations are noted), balance eccentricity and linearity (these 

factors are considered as a part of the measurement process when obtaining the 

standard deviation of the process when using a check standard with adequate 

degrees of freedom.

NOTE: Where inadequate degrees of freedom are available, k, is determined using 

the appropriate degrees of freedom and the 95.45 % column in the table from 

Appendix A of NISTIR 6969, SOP 29.

6 Certificate

Report results as described in SOP No. 1, Preparation of Calibration Certificates.

Report the mass (if appropriate and requested by the customer), conventional mass, 

environmental conditions during the calibrations, mass density used (reported, 

measured, or assumed), and calculated expanded uncertainties with coverage 

factor(s).

Conformity assessments.

Evaluate compliance to applicable tolerances as needed or required by the customer 

or by legal metrology requirements. Decision criteria for uncertainty and tolerance 

evaluations include two components: 1) the expanded uncertainty, U, must be < 1/3 

of the applicable tolerances published in ASTM E617 and OIML R111 

documentary standards and 2) the absolute value of the conventional mass 
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correction value plus the expanded uncertainty must be less than the applicable 

tolerance to confidently state that mass standards are in or out of tolerance. 

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

Single Substitution Data Sheet

(Optional Sequence A, SXX)

Laboratory data and conditions:

Operator Before After

Date Temperature

Balance Pressure

Load Relative Humidity

Standard deviation of the process, 

from control chart, sp Degrees of Freedom

Mass standard(s) data:

ID Nominal Mass 

Correction

Unc:

From cal. 

certificate

Unc:

k factor

Density

g/cm3

Unc of 

Density 

(k=1)

S

ts

X

tx

Sc

tSc

sw

Mass Correction = True Mass if using buoyancy correction. Mass Correction = Conventional Mass if NOT using buoyancy 

correction. Density is used only with buoyancy corrections.

Observations:

Measurement # Weights Balance Observations, Units __________

Time:

1 (O1) S + ts

2 (O2) X + tx

3 (O3) X + tx + sw

Time:

Measurement Assurance (See Section 4.5):

Measurement # Weights Balance Observations, Units __________

Time: 

1 (O1) S + ts

2 (O2) Sc + tSc

3 (O3) Sc + tSc + sw

Time: 

Check Standard in Control? _____Yes_____No
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Appendix B

Single Substitution Data Sheet

(Optional Sequence B, XSS)

Laboratory data and conditions:

Operator Before After

Date Temperature

Balance Pressure

Load Relative Humidity

Standard deviation of the process, 

from control chart, sp Degrees of Freedom

Mass standard(s) data:

ID Nominal Mass 

Correction

Unc:

From cal. 

certificate

Unc:

k factor

Density

g/cm3

Unc of 

Density 

(k=1)

S

ts

X

tx

Sc

tSc

sw

Mass Correction = True Mass if using buoyancy correction. Mass Correction = Conventional Mass if NOT using buoyancy 

correction. Density is used only with buoyancy corrections.

Observations:

Measurement # Weights Balance Observations, Units __________

Time:

1 (O1) X + tx

2 (O2) S + ts

3 (O3) S + tS + sw

Time:

Measurement Assurance (See Section 4.5):

Measurement # Weights Balance Observations, Units __________

Time: 

1 (O1) S + ts

2 (O2) Sc + tSc

3 (O3) Sc + tSc + sw

Time: 

Check Standard in Control? _____Yes_____No
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This publication is available free of charge from: https://doi.org/10.6028/NIST.IR.6969-2019