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SOP 19 

Standard Operating Procedure for 

Calibration of Graduated Neck-Type Metal Provers

(Volume Transfer Method)1

1 Introduction 

Purpose of Test 

This procedure is used to calibrate graduated neck type metal test measures and 

provers (20 L (5 gal) and larger) that are used in verification of petroleum,

biodiesel, ethanol, milk, and/or water meters. Detailed measurement ranges, 

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

separate document in the laboratory. 

Conformity Assessment 

Standards that are calibrated for use in legal weights and measures applications 

should be evaluated for conformance to the appropriate specifications and 

tolerances that apply. Test measures or provers being calibrated should be evaluated 

using the checklist provided in NIST Handbook 105-3, Specifications and 

Tolerances for Graduated Neck Type Volumetric Field Standards, 2010. 

Alternatively, if requested by the customer, evaluation against OIML R 120 (2010),

Standard capacity measures for testing measuring systems for liquids other than 

water, may be referenced. Where compliance is required by law, conformity

evaluations should be conducted prior to performing calibrations. See Section 6.2

for reporting results.

Prerequisites

Verify that the unknown prover has been properly cleaned and vented, with 

all petroleum products removed prior to submission for calibration to ensure 

laboratory safety and compliance with environmental disposal 

requirements. The prover may be visually inspected to determine that

residual liquid petroleum products are not present. Smell is not necessarily 

an adequate indicator of cleanliness. 

Note: Many laboratories have a policy regarding cleanliness of submitted 

volumetric standards to minimize water contamination with flammable 

petroleum products.

Verify that valid current calibration certificates with measurement values 

and uncertainties are available for all the standards used in the test. All 

calibration values must have demonstrated metrological traceability to the 

1 Non-SI units are predominately in common use in State legal metrology laboratories, and/or the petroleum industry

for many volumetric measurements, therefore non-SI units have been used to reflect the practical needs of the

laboratories performing these measurements as appropriate.

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international system of units (SI). Metrological traceability may be to the SI

through a National Metrology Institute such as NIST.

Verify that the standards to be used have sufficiently small standard 

uncertainties for the intended level of calibration.

Verify the availability of an adequate supply of clean, preferably soft water 

(filtered and thermally equilibrated, as appropriate) water (GLP 10). Water 

does not need to be distilled or deionized for use in this procedure. The 

equations used in GLP 10 for the calculation of water density (air saturated) 

may be used without a significant impact on the measurement results.

Verify that the operator has had specific training and is proficient in SOP 

17, SOP 19, SOP 20, SOP 31, GMP 3, and is familiar with the operating 

characteristics and conditioning of the standards used.

Verify that the laboratory facilities meet the following minimum conditions 

to make possible the expected uncertainty achievable with this procedure: 

Table 1. Laboratory environmental conditions.

Procedure Temperature Relative Humidity 

Volume Transfer 18 C to 27 C 

Stable to ± 2.0 C / 1 h 

35 % to 65 % 

Stable to ± 20 % / 4 h 

Field Calibrations (Tests) 

A “field” calibration is considered one in which a calibration is conducted

in uncontrolled environments, such as out-of-doors. Calibrations conducted 

under field and laboratory conditions are not considered equivalent.

The care required for field calibrations includes proper safety, a clean and 

bubble-free water supply, measurement control programs, and a stable

temperature environment shaded from direct sunshine to allow the prover,

field standard, and clean test liquid (water) to reach an equilibrium

temperature with minimal evaporation. Environmental conditions must be

selected to be within stated laboratory conditions during the measurements.

All data and appropriate environmental conditions must be documented 

regardless of test location. 

An increased number of check standard verifications are required to ensure 

continued suitability of calibration values generated in field conditions as 

well as to verify the validity of any standards taken out of a secure 

laboratory environment once the standard(s) are returned to the laboratory.

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2 Methodology 

Scope, Precision, Accuracy 

This procedure is applicable for the calibration of any size metal prover

within the limitations of the standards available. The repeatability attainable 

depends on strict adherence to the procedure, the care in volumetric 

adjustments, and the number of transfers, in the case of multiple transfers. 

The accuracy depends on the standards used.

Summary 

Water is delivered from calibrated volumetric standard(s) into the unknown 

test measure or prover being calibrated. Depending on the respective 

volumes, multiple transfers may be required. While these should be

minimized, a maximum number of 15 transfers are permitted to ensure that 

final uncertainties and systematic errors are sufficiently small for the 

intended applications. The temperature of the calibration medium (water) 

cannot be considered constant during transfers; hence, the temperature of 

the water for each transfer must be measured. Because of the large volumes, 

the difference in thermal expansion of the respective vessels must be

considered. Hand held test measures require a 30 s (± 5 s) pour followed by

a 10 s drain, with the measure held at a 10° to 15° angle from vertical, during

calibration and use. Provers are emptied by gravity drain, followed by a 30 

s final drain after the cessation of flow.

Standards and Equipment 

Calibrated volumetric standards of suitable sizes. 

Calibrated flask(s) of suitable sizes to calibrate neck of prover.

A funnel for transferring water from the flask into the prover or test 

measure. 

Meniscus reading device (See GMP 3).

Calibrated thermometer, with resolution and uncertainty less than 0.1 C.

Timing device (calibration is not required; uncertainty of the measurement 

only needs to be less than 5 s for a 30 s pour time or drain time).

Sturdy platform, with appropriate safety conditions, with sufficient height 

to hold standard and to permit transfer of water from it to the prover by

gravity flow.

Clean pipe or tubing (hoses) to facilitate transfer of water from the

laboratory standard to prover. Pipe and hose lengths must be minimized to 

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reduce water retention errors. Care must be taken during wet-downs and 

runs to ensure complete drainage and consistent retention in all hoses or

pipes.

Procedure

Cleanliness verification

Fill and drain both the standard and unknown test measure or prover to be 

calibrated and check for visual evidence of soiling and of improper drainage. If necessary, clean with non-foaming detergent and water and rinse 

thoroughly (see GMP 6).

Neck scale plate calibration

Neck scale plate calibrations are generally conducted only for new or 

damaged volumetric measures, those that have not been calibrated by the 

laboratory in the past, or those for which the calibration data is not available. 

See SOP 31 for the neck scale plate calibration procedure.

Body Calibration

2.4.3.1 Fill the standard with water and then transfer the water into the 

unknown prover establishing a wet down of the standard. Wait 30 s 

after the cessation of the main flow on the standard before closing 

the drain valve. Level the unknown prover, and drain or empty the 

water, following the applicable emptying and draining procedure

based on the standard being calibrated. Hand held test measures

require a 30 s (± 5 s) pour followed by a 10 s drain, with the measure 

held at a 10° to 15° angle from vertical, during calibration and use.

Provers are emptied by gravity drain, followed by a 30 s final drain 

after the cessation of the main flow. 

2.4.3.2 If a bottom zero is present, follow the guidance provided in SOP 

21 for LPG provers as follows: When the liquid reaches the top of 

the lower gauge glass, close the valve and allow the water to drain

from the interior of the prover into the lower neck for 30 s. Then

bleed slowly with the bleed valve (4) until the bottom of the liquid 

meniscus reaches the zero graduation. (This step should be started

during the 30 s drain period but should not be completed before the

end of the drain period).

Alternatively, the prover may be completely drained with a 30 s drain time 

after the cessation of the main flow, and then refilled with a funnel 

and small volume of water to set the zero mark (which will add to 

the prover calibration uncertainty due to variable retention

characteristics).

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2.4.3.3 Run 1. Fill the standard and measure and record the temperature, 

t1. 

2.4.3.4 Adjust the standard prover to its reference mark or record the neck 

reading, and then discharge into the unknown prover. Wait 30 s 

after cessation of the main flow to attain specified drainage, and 

then close the delivery valve. Remove any hoses or pipes to prevent 

additional water transfer. 

2.4.3.5 Repeat step 2.4.3.4 as many times as necessary (note the 15-drop 

limit) to fill the unknown prover to its nominal volume. Verify the 

level condition and record the temperature of water in the standard 

for each drop, t1 to tN. 

2.4.3.6 Level the filled unknown prover. Check the prover level by placing 

a precision spirit or electronic digital level vertically on the neck 

on at least two locations, 90° apart around the circumference of the 

neck and adjust the orientation of the unknown measure until the 

neck is as close to vertical (plumb or perpendicular to the horizontal 

plane) as possible. Verify and adjust any mounted levels that are on 

the prover to agree (when present and when possible). 

2.4.3.7 Read and record the scale plate (gauge) reading. 

2.4.3.8 Measure the temperature of the water in the unknown prover, tx,

and record. For test measures without thermometer wells, the 

temperature should be taken as close as possible to the center 

(vertically and horizontally) of the cylinder of the test measure

main body (and not in the neck). For larger provers, and when 

thermometer wells are present, the average temperature, calculated

from temperatures taken at multiple locations from within the 

unknown prover should be used. (Alternatively, if a prover has 

mounted thermometers, the internal temperature from multiple 

locations within the prover may be used). 

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2.4.3.9 Perform the calculations described in section 3 to determine the 

prover volume at the appropriate reference temperature. 

2.4.3.10Adjust the scale as needed. If adjusted, record the adjusted prover 

gauge reading for determining the “as left” value for Run 1. Run 2 

will validate the setting. Alternatively, the average of Run 1 and 

Run 2 may be used with the adjustment made after Run 2. In that

case, a validation run (Run 3) is required to ensure correct setting 

of the scale plate.

2.4.3.11Run 2 - Repeat the process described from 2.4.3.3 to 2.4.3.9. 

Replicate runs of the test measure or prover (when the volume is 

corrected to the reference temperature) must pass the F-test, agree 

within ± 0.02 % of the test volume, or be within the control/action

limits on the standard deviation or range charts (whichever is the

most rigorous assessment). When calculating a 0.02 % agreement,

it is calculated as the difference between Run 1 and Run 2, divided

by the nominal volume, and then multiplied by 100. 

Note: If excess disagreement between replicated measurements is

observed, check all vessels for cleanliness, leaks, drain lines, 

additional valve, or damage, identifying and correcting any

problems. Lack of measurement agreement may be due to prover 

condition, contamination, lack of cleanliness, excessive temperature 

changes, poor laboratory conditions, or poor field conditions, such

as when calibration is conducted in an unstable environment.

Repeatability problems must be corrected before calibration can be

completed. 

2.4.3.12Seal the equipment as specified in the laboratory policy.

3 Calculations 

The following calculations assume that the standard was calibrated using a reference 

temperature of 60 °F (15.56 °C) and that you are calibrating a field standard to a reference 

temperature of 60 °F (15.56 °C). Equations for situations where different reference 

temperatures are involved follows in Section 3.4.

Single Delivery 

Calculate VX60, the volume of the unknown prover at 60 F, using the following 

equation:

1 VS 60  1 



1 t 1  60 F

 VX 60  Eqn. (1) 

 x 



1  tx  60 F



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Multiple Deliveries 

Calculate VX60, the volume of the unknown prover at 60 F, using the following 

equation:

1 V S 60+1



1t 1

  60 F

 2V S 60  2



1 t 2   60 F

 ... N S V 60  N 



1 t N 

  60 F

 VX 60    1 t   60 F x  x 

Eqn. (2) 

Table 2.Variables for VX60 equations. 

Variables Used in Volume Equations 

VX60 volume of the unknown vessel at 60 F

VS60 volume of the standard vessel at 60 F

1,2,...,N 

density of the water in the standard prover where 1 is the density of the water for the 

first delivery, 2 is the density of the water for the second delivery, and so on until all 

N deliveries are completed

1, 2,..., N 

volume difference between water level and the reference mark on the standard where 

the subscripts 1, 2,..., N, represent each delivery as above. If the water level is below

the reference line,  is negative. If the water level is above the reference line,  is 

positive. If the water level is at the reference line,  is zero

Note: units must match volume units for the standard. The  is zero for slicker-plate 

type standards.

t1, t2, ..., tN temperature of water for each delivery with the subscripts as above

 coefficient of cubical expansion for the standard in units / oF

ß coefficient of cubical expansion for the prover in units / oF

tx temperature of the water in the filled unknown vessel in units oF

x density of the water in the unknown vessel in g/cm3

Note: Values for the density of water should be calculated from the equations given in GLP 10. The 

cubical coefficient of the materials must match the unit assigned to the temperature measurement.

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Prover Error/Correction or Deviation from Nominal

The total calculated volume of the prover at its reference temperature should

be reported on the calibration report. The SI unit of volume is m3

, so a

conversion factor is to be included on the report in the notes section when 

other volume units are used. 

The prover volume for an open neck prover equals the VX60 value minus the 

gauge reading that is the difference from the nominal volume (with matched 

units).

Prover volume  V gauge reading X 60 Eqn. (3) 

Prover error  Prover volume V Nom Eqn. (4) 

Prover error V gauge reading V X 60 Nom Eqn. (5) 

where: VNom = Nominal volume (taking care to match units).

VX60 is the calculated volume of water delivered from the standard that 

should be observed in the unknown prover. A positive prover error means 

that the prover is larger than nominal. A negative prover error means that 

the prover is smaller than nominal.

Example 1: If VX60 is 100.02 gal and gauge reading is 0.02 gal (above 

nominal); then the prover volume at nominal is 100.00 gal; and the prover 

error and correction are 0; and no adjustment is needed.

Example 2: If VX60 is 100.02 gal and gauge reading is -0.02 gal (below 

nominal); then the prover volume at nominal is 100.04 gal; the prover error

is + 0.04 gal; and to adjust the prover, set the gauge to read 0.02 gal (the

volume level will show a gauge reading of 0.02 gal, which is 4.62 in3 or 

about 5 in3, above nominal).

Alternative Reference Temperatures

Reference temperatures other than 60 oF (15.56 oC) may occasionally be 

used. Common reference temperatures for other liquids follow, however not

all of them may be suitable for use with standards calibrated using this 

procedure:

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Table 3. Common reference temperatures.

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Commodity Reference Temperature

Frozen food labeled by volume (e.g., fruit juice) -18 oC (0 oF)

Beer 3.9 oC (39.1 oF)

Food that must be kept refrigerated (e.g., milk) 4.4 oC (40 oF)

Distilled spirits or petroleum 15.56 oC (60 oF)

Petroleum (International Reference) 15 oC (59 oF)

Compressed Natural Gas (CNG) 15 °C (60 oF)

Wine 20 oC (68 oF)

Unrefrigerated liquids (e.g., sold unchilled, like soft drinks) 20 oC (68 oF)

Hydrogen (H2) 21 oC (70 oF)

Petroleum (Hawaii) 26.67 oC (80 oF)

Equations for calculations when using alternative reference temperatures

follow: 

3.4.2.1 Single Delivery 

Calculate VXtref, the volume of the unknown prover at its designated 

reference temperature (F), using the following equation:

 V   



1 t  t  1 S tref 1 1 ref S  V  Eqn. (6) Xtref  x 



1  tx  tref X 



3.4.2.2 Multiple Deliveries 

Calculate VXtref, the volume of the unknown prover at its designated 

reference temperature, using the following equation:

        V    1  t t  V  1   t t ... V  1 t t 1  StrefS 1                1 1 ref S  2 Stref S 2  2 2 ref S  N Stref S N  N N ref S  V  Xtref X    1 tt     x   x ref X 

Eqn. (7)

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Table 4 Variables for volume equations at alternative temperatures.

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Symbols Used in Equations 

VXtrefX volume of the unknown vessel, VX at its designated reference temperature, tref X 

VStrefS volume of the standard vessel, VS at its designated reference temperature, tref S 

ρ1, ρ2, ρ3 

density of the water in the standard where 1 is the density of the water for the first 

delivery, 2 is the density of the water for the second delivery, and so on until all N 

deliveries are completed 

1, 2,..., N 

volume difference between water level and the reference mark on the standard where

the subscripts 1, 2,..., N, represent each delivery as above. If the water level is below 

the reference line,  is negative. If the water level is above the reference line,  is

positive. If the water level is at the reference line,  is zero. Note: units must match 

volume units for the standard. The  is zero for slicker-plate type standards.

t1, t2, ..., tN temperature of water for each delivery with the subscripts as above 

 coefficient of cubical expansion for the standard in its designated units 

ß coefficient of cubical expansion for the prover in its designated units

tx temperature of the water in the filled unknown vessel in designated units 

x density of the water in the prover in g/cm3

Notes: Values for the density of water should be calculated from the equations given in GLP 10. The 

cubical coefficient of the materials must match the unit assigned to the temperature measurement. 

Calculate the within process standard deviation, sw, for the replicate runs. For two 

runs, the degrees of freedom will be one. This value is plotted on the standard 

deviation chart and may be used to incorporate an F-test as well.

The range of the replicated runs must repeat within 0.02 % of the volume, or the 

standard deviation must be less than applicable control/action limits on standard

deviation charts, or the observed standard deviation must pass the F-test statistics 

(as applicable). Where the F-test is used, calculate the F statistic to compare the

observed within process standard deviation, sw, to the accepted (pooled) within 

process standard deviation for the measurement process. (See NISTIR 6969, 

Sections 8.4 and 8.9.2, for more information on pooling standard deviations and Ftests).

2

s w Observed F  2 Eqn. (8) 

s w Accepted

The calculated F statistic must be less than the F value obtained from an F table at 

95 % confidence level (Table 9.12, NISTIR 6969) to be acceptable. The F value is 

obtained from the F table for one degree of freedom for the numerator and the 

degrees of freedom for the denominator is equal to the number of degrees of 

freedom in the pooled within process standard deviation. If the data fails the 

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repeatability assessments and the source of the error cannot be determined 

conclusively and corrected, the measurement must be repeated. All values must 

be entered in the standard deviation chart or control chart, even if failing the 

repeatability assessment to ensure the variability of the accepted measurement 

process is representative of the process and not unduly reduced over time. 

Calculate and report the mean volume of the volumetric standard at its applicable

reference temperature.

If adjustments were made during replicate runs, report the “as found” volume or

the mean of “as found” volumes and the “as left” volume or mean of “as left” 

volumes, as applicable, at the appropriate reference temperature. (Do not calculate 

a mean value by combining “as found” and “as left” values when adjustments are 

made).

4 Measurement Assurance 

Duplicate the process with a suitable check standard. See SOP 17 or SOP 30. Plot 

the check standard volume and verify that it is within established limits. The mean 

of the check standard observations may be used to evaluate bias and drift over time 

when a reference value for the check standard is available. Check standard 

observations are used to calculate the standard deviation of the measurement 

process which contributes to the Type A uncertainty components.

A t-test may be incorporated to check the observed value against an 

accepted value. 

S  S  c c t  Eqn. (9) 

s p 

The t-statistic is evaluated using Eqn. 9 with a 95 % confidence level. All 

values must be entered in the control chart, even if failing this statistic to 

ensure the variability obtained for the process is truly representative of the

process and 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. The limits for the t-test are based on applicable warning and action 

limits on the control chart (The applicable limits are shown in SOP 20 and

based on the number of replicates).

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A standard deviation chart is also used for measurement assurance through the 

evaluation of replicate measurements (See SOP 20). The standard deviation of each 

combination of Run 1 and Run 2 is calculated and the pooled standard deviation 

over time may be used to estimate the short-term variability in the measurement

process. A standard deviation chart for unknown provers represents the variability

in condition of test measures submitted for calibration as well as the short-term 

repeatability of the measurement process but does not monitor the stability of the 

reference standard or represent the variability or potential systematic errors 

associated with meniscus readings (See GMP 3). The range of the calculated

measurement results must agree to within 0.02 % of the volume, or the standard 

deviation must be less than applicable control/action limits on standard deviation 

charts, or the observed standard deviation must pass the F-test statistics (as 

applicable).

For unknown standards that are adjusted, do not combine an “as found” value with 

an “as left” value for the two runs entered into the chart; use the adjusted value 

from Run 1 and the value from Run 2, both at the applicable reference temperature,

when entering values in a standard deviation or range chart.

5 Assignment of Uncertainties

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

laboratory volumetric standards used, us, plus the standard deviation of the process, sp, and 

the additional items noted below and in the uncertainty budget table, Table 5, at the 95 %

level of confidence. See NISTIR 6969, SOP 29 for the complete standard operating 

procedure for calculating the uncertainty. 

The standard uncertainty for the standard, us, 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 need 

to be divided by the associated coverage factor k. See SOP 29 for the complete 

standard operating procedure for calculating the uncertainty when multiple

deliveries or multiple standards are used to ensure correct handling of correlated 

uncertainties. Fifteen is the maximum recommended number of deliveries from a

laboratory standard to a prover under test to minimize calibration uncertainties to

the levels identified previously.

The standard deviation of the measurement process, sp, is taken from a control chart 

for a check standard or from standard deviation charts from provers of similar size. 

See SOP 17, SOP 20 and NISTIR 6969, SOP 30. The larger of the value from the 

standard deviation over time for a check standard or from the standard deviation 

chart should be used in the uncertainty calculations. If a check standard is available,

it is possible to evaluate the presence of bias in the measurement process. Where 

multiple staff members perform this calibration and obtain values for the check

standard, the standard deviation for a check standard may represent variability and

systematic errors associated with the meniscus reading. When a standard deviation 

chart is used alone (i.e., a check standard is not used), the repeatability represents

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the process only and does not represent potential systematic differences in meniscus 

readings. In a laboratory with only one staff member performing calibration and 

entering data for a check standard, additional uncertainties for meniscus readings 

are needed per Section 5.3 and GMP 3.

Neck calibration uncertainty should be estimated based on the uncertainty of 

standards used, errors observed during calibration, ability to read the meniscus of

all standards involved (see GMP 3) and the repeatability of the neck calibration (see 

SOP 31). 

Other standard uncertainties usually included at this calibration level primarily

include 1) uncertainties associated with the ability to read the meniscus, only part 

of which is included in the process variability due to parallax and visual capabilities

(unless multiple staff are represented with a check standard that demonstrates

variability is meniscus readings), and 2) uncertainties associated with temperature

corrections that include values for the cubical coefficient of expansion for the 

prover under test, the accuracy and gradients associated with temperature

measurements in test measures or provers. Additional factors that might be included 

are: round robin or proficiency testing data showing reproducibility, environmental 

variations over time, and bias or drift of the standard as noted in control charts.

To properly evaluate uncertainties and user requirements (tolerances), assessment 

of additional user uncertainties may be required by laboratory staff. Through proper 

use of documented laboratory and field procedures, additional uncertainty factors 

may be minimized to a level that does not contribute significantly to the previously 

described factors. Additional standard uncertainties in the calibration of field 

standards and their use in meter verification may include: how the prover level is 

established, how delivery and drain times are determined, the use of a proper 

“wetted-down” prior to calibration or use, whether gravity drain is used during 

calibration or whether the volume of water is eliminated by pumping, the 

cleanliness of the prover and calibration medium, prover retention characteristics

related to inside surface, contamination or corrosion, and total drain times, and 

possible air entrapment in the water, and connecting pipes. Systematic errors may 

be observed between laboratory calibration practices where a gravity drain is used 

and field use where the pumping system is used. 

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

Table 5. Multiple values of some items may need to be considered (e.g., multiple 

drops from the standard, multiple meniscus readings, and multiple temperature

readings).

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Table 5. Example Uncertainty Budget Table. 

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Uncertainty Component Description Symbol Source Typical 

Distribution

Uncertainty of the standard (5.1) us 

Calibration certificate(s); 

may be multiplied or added 

based on dependencies

Expanded divided 

by coverage factor

Accepted standard deviation of the 

process (5.2) sp 

Control chart, standard 

deviation chart Normal

Uncertainty or uncorrected error 

associated with a neck calibration (5.3) un SOP 31 Rectangular

Ability to read the Meniscus in S (5.4) um 

None if using a slickerplate type standard; GMP 3 Triangular

Ability to read the Meniscus in X (5.4) um GMP 3 Triangular

Water temperature (S) (5.4) uts 

Consider accuracy, 

resolution, and gradients Rectangular

Water temperature (X) (5.4) utx 

Consider accuracy, 

resolution, and gradients Rectangular

Cubical Coefficient of Expansion (CCE) 

on S (5.4) uCCE 

5 % to 10 % of the CCE 

(EURAMET CG-21) Rectangular

Cubical Coefficient of Expansion (CCE) 

on X (5.4) uCCE 

5 % to 10 % of the CCE 

(EURAMET CG-21) Rectangular

Uncertainty of bias, drift, or variability

of standards (5.2) ub 

From control charts or 

calibration history of 

reference standards

Rectangular

Uncertainty of drain time (insignificant 

if closely following the procedure) ud From experimental data Normal

Uncertainty Evaluation

Where applicable, uncertainties for volume calibrations that are assessed for 

conformity must be less than the tolerances specified in Handbook 105-3 and used 

for decision rules.

6 Calibration Certificate

Report results as described in SOP 1, Preparation of Calibration Certificates, with

the addition of the following: 

“To Contain” or “To Deliver” prover volume, reference temperature, uncertainty,

material, thermal coefficient of expansion (based on identification plate), 

construction, any identifying markings, tolerances (if appropriate), laboratory 

temperature, water temperature(s) at time of test, barometric pressure, relative 

humidity, and any out–of-tolerance conditions. Appendix B, Example Temperature 

Correction Chart may be provided as a supplement to the calibration report to 

encourage appropriate volumetric corrections of the provers during routine use.

SOP 19 – 2019 Page 14 of 18
 

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Conformity Assessment 

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

or by legal metrology requirements. Compliance assessments must note the 

applicable documentary standard and which portions of the standard were or were 

not evaluated. The uncertainty for volume calibrations must be less than the 

tolerances published in the applicable documentary standards. For volume

calibrations where the unknown standard can be adjusted, it is standard practice to 

adjust the standard or leave the scale plate in a position close enough to its nominal 

volume to ensure that the absolute value of the measurement result plus the

uncertainty is less than the applicable tolerance. Where the unknown standard 

cannot be adjusted, and a portion of the uncertainty band from the error exceeds

tolerance limits, it is not appropriate to state compliance with the tolerances unless

additional decision rules are communicated with and agreed to by the end user.

Correction values (measurement results) may need to be used by the end user in

such cases.

7 Additional References:

Bean, V. E., Espina, P. I., Wright, J. D., Houser, J. F., Sheckels, S. D., and Johnson, A. N., NIST 

Calibration Services for Liquid Volume, NIST Special Publication 250-72, National Institute of 

Standards and Technology, Gaithersburg, MD, (2009).

EURAMET Calibration Guide 21, Guidelines on the Calibration of Standard Capacity Measures

Using the Volumetric Method (Version 1.0, 04/2013).

SOP 19 – 2019 Page 15 of 18
 

 

 

 

 

 

 

 

 

 

Appendix A 

Volume Transfer Data Sheet (page 1) 

Laboratory data and conditions:

This publication is available free of charge from: https://doi.org/10.6028/NIST.IR.7383 -2019

Vessel Owner Operator

Vessel Identification Date

Nominal Volume Air Temperature

Material Relative Humidity

Cubical Coefficient of 

Expansion

Standard deviation of the process, sp 

from Control Chart

Reference temperature of 

unknown prover

Standard deviation of the process, sp 

from the Standard Deviation Chart

Unknown prover graduations Degrees of Freedom

Applicable specifications and 

tolerances 

Volume standard(s) data: 

Identification (ID)

(Note ID of 

Standards)

Nominal 

Volume Volume/Correction Expanded Unc: From Cal. Cert.

Unc:

k factor 

Cubical 

Coefficient of 

Expansion

S

S

S

S

Run 1: Data for volumes delivered from the standards: 

DROP 

# 

Reported Volume 

(gal) Material (MS/SS) Water Temp (°C) 

(Must be ≥ 0.5 °C and < 40 °C)

Gauge 

Delta 

(in3)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

SOP 19 – 2019 Page 16 of 18
 

 

 

This publication is available free of charge from: https://doi.org/10.6028/NIST.IR.7383 -2019

Appendix A 

Volume Transfer Data Sheet (page 2) 

Run 1: Data from the filled unknown field standard: 

Material for the Unknown: MS, SS, TP, PV

Final Gauge Reading: in3

Final Water Temperature: °C

Run 2: Data for volumes delivered from the standards: 

DROP 

# 

Reported Volume 

(gal) Material (MS/SS/)

Water Temp (°C) 

(Must be ≥ 0.5 °C and < 40 

°C) 

Gauge Delta 

(in3)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Run 2: Data from the filled unknown field standard: 

Material for the Unknown: MS, SS, TP, PV

Final Gauge Reading: in3

Final Water Temperature: °C

SOP 19 – 2019 Page 17 of 18
 

Appendix B 

Example Temperature Correction TableA

This publication is available free of charge from: https://doi.org/10.6028/NIST.IR.7383 -2019

Example for a 100 gallon prover and 60 °F reference temperature. 

Mild Steel 

CCE: 1.86 x 10-5 / °F

Stainless Steel 

CCE: 2.65 x 10-5 / °F

Temperature °F in3 gal in3 gal

-20 -34 -0.149 -49 -0.212

-15 -32 -0.139 -46 -0.199

-10 -30 -0.130 -43 -0.186

-5 -28 -0.121 -40 -0.172

0 -26 -0.112 -37 -0.159

5 -24 -0.102 -34 -0.146

10 -21 -0.093 -31 -0.133

15 -19 -0.084 -28 -0.119

20 -17 -0.074 -24 -0.106

25 -15 -0.065 -21 -0.093

30 -13 -0.056 -18 -0.079

35 -11 -0.047 -15 -0.066

40 -9 -0.037 -12 -0.053

45 -6 -0.028 -9 -0.040

50 -4 -0.019 -6 -0.026

55 -2 -0.009 -3 -0.013

60 0 0.000 0 0.000

65 2 0.009 3 0.013

70 4 0.019 6 0.026

75 6 0.028 9 0.040

80 9 0.037 12 0.053

85 11 0.046 15 0.066

90 13 0.056 18 0.080

95 15 0.065 21 0.093

100 17 0.074 24 0.106

105 19 0.084 28 0.119

110 21 0.093 31 0.133

115 24 0.102 34 0.146

120 26 0.112 37 0.159

CCE = coefficient of cubical expansion 

A Provide only the applicable coefficient of cubical expansion for the prover under test.

SOP 19 – 2019 Page 18 of 18