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GLP 1 

Good Laboratory Practice

for the

Quality Assurance of Laboratory Measurement Results1

Quality assurance of laboratory measurement results (measurement assurance) means 

understanding, modeling, measuring, and managing a measurement assurance system appropriate 

to the laboratory’s scope of activities. Having such a system in place will allow the laboratory to 

know, within the limits of a measurement process, that measurement results are valid with respect 

to stated traceability, accuracy, and precision. A well-designed measurement assurance system 

provides confidence and credibility in the quality of the laboratory’s measurement results by 

ensuring that the measurement results are metrologically traceable to appropriate reference 

standards and measurement units, with suitably valid uncertainties. 

Quality assurance (QA) and quality control (QC) methods should consider both internal and 

external data for evaluating the ongoing stability and control of the measurement results and 

processes. At its core, the concept of measurement assurance is one of risk identification and 

mitigation. It provides methods for monitoring the standards and as well as the measurement 

process, and varying combinations of each depending on the priorities of the methods chosen. 

Software quality assurance is a key function of ensuring the quality of laboratory measurement 

results but is outside the scope of this procedure. 

1 Internally Obtained Measurement Assurance Data

The validity of calibrations needs to be monitored with quality control procedures. Statistical 

techniques are used to record, analyze, and monitor charted measurement results to permit the 

ongoing assurance of valid and stable measurement results, integration of intermediate checks, 

and/or the detection of trends. The metrologists and laboratory management should also plan and 

review the results from quality assurance monitoring as methods are integrated into calibration 

procedures and during periodic management reviews and internal assessments (internal audits).

Steps taken to ensure the quality of the measurement process may include, but are not limited to:

a. Regular use of reference materials or quality control; 

b. Regular use of alternative instrumentation that has been calibrated to provide traceable 

results;

c. Functional checks of measuring and testing equipment;

d. Use of check or working standards with control charts, where applicable;

e. Periodic intermediate checks on measuring equipment;

f. Replicate tests or calibrations using the same or different methods, with the use of 

standard deviation charts or range charts where applicable;

g. Retesting or recalibration of retained items (e.g., customer items that are not 

immediately returned);

h. Correlation of results for different characteristics of an item;

i. Review of reported data by competent laboratory personnel;

 1 See also Section 7.7 of ISO/IEC 17025:2017 General Requirements for the Competence of Testing and Calibration Laboratories.
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j. Intralaboratory comparisons; and

k. Blind tests. 

Each measurement parameter in the laboratory’s scope of activities must be reviewed and analyzed 

to determine the validity of the measurement process.

The standards and the measurement process for each parameter must be in a state of statistical 

control. Statistical control means that the variability of the measurement process is known, stable

and observed values are adequately close to reference values, within the chosen statistical limits. 

When a process is in statistical control and the reference values are within suitable limits, we can 

assume that the reported measurement uncertainties are valid. 

Minimizing risks of measurement errors includes all the following laboratory functions:

a. Training staff and evaluating effectiveness and proficiency; 

b. Monitoring the laboratory environment to minimize potential errors or excess 

variation;

c. Maintaining suitable equipment (including installation, monitoring, approvals, and 

integrated software); 

d. Selecting and calibrating standards; 

e. Ensuring suitable suppliers for materials and calibrations; 

f. Selecting and validating procedures with evaluation of accuracy/bias and precision; 

g. Ensuring proper care and handling of laboratory standards, equipment, and items 

submitted for calibration; 

h. Accurately and effectively calculating, evaluating, and reporting measurement 

uncertainty;

i. Participating in inter- and intra-laboratory comparisons; 

j. Creating and reviewing calibration certificates to ensure accuracy of measurement 

results and the effective communication of results; and

k. Controlling data – information management (including software and information 

technology controls).

While other quality assurance methods could meet these objectives, the control programs 

developed for measurement assurance greatly increase the comprehensiveness of the program.

2 Externally Obtained Data Used for Measurement Assurance

Data from measurement results obtained external to the laboratory need to be considered when 

evaluating the quality control and measurement assurance. Such steps that may be taken include:

a. Evaluation of the calibration history of reference standards, working standards, and 

check standards; 

b. Evaluation of before/after calibrations within a laboratory to compare and evaluate 

results obtained from an external calibration provider; 

c. Review of historical calibration data for items calibrated having demonstrated stability;

d. Comparison of all calibration results and calibration history on control charts for 

working standards and check standards with results from external calibration sources;

e. Participation in proficiency testing using the same procedures and handling methods 

used for routine laboratory calibrations; 
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f. Use of externally obtained data from calibrations, proficiency tests, and interlaboratory 

comparisons in the assessment of errors and bias in measurement results; and 

g. Participation in interlaboratory comparisons other than proficiency testing (e.g., for 

method validation or as a training activity).

Data from all the measurement assurance activities should be analyzed and monitored to both 

control and improve the laboratory's activities, if applicable. When the results of the data analyses 

from monitoring activities are found to be outside pre‐defined criteria, appropriate actions shall be 

taken to prevent incorrect results from being reported to the customer.

The strength of the measurement assurance approach lies in its applicability to a wide variety of 

measurements with sufficient flexibility to permit each measurement control program to be 

tailored to the needs of a given measurement area. The sophistication of the control program 

depends on the criticality of the measurement. 

3 Integration of Data from Multiple Sources

Measurement results collected over several years may be statistically evaluated with current results 

being compared to results from previous years. Any observed problems or changes in the 

measurement results are investigated and, as appropriate, corrective action taken. Ongoing 

monitoring establishes a continuous and comprehensive internal laboratory measurement 

assurance program. 

Data from internal measurement assurance programs should be compared to the results of 

calibration history assessments, interlaboratory comparisons or proficiency tests, and other 

external sources of data.

Data and analysis from the integrated assessment of measurement assurance data provides 

assurance of measurement quality, provides input to and validation of measurement uncertainties, 

supports selection and adjustment of calibration intervals for standards and laboratory instruments, 

and provides a graphical and statistical basis for evaluating and making decisions regarding the 

quality of measurement results.

4 NIST Office of Weights and Measures Resources 

The National Institute of Standards and Technology (NIST) provides technical guidance and 

support to laboratories to develop suitable measurement control programs that provide a systems 

approach to measurement assurance as a part of published resources and training seminars. 

Objectives to evaluate the entire measurement process, as a system or as a production process, will 

consider all the following:

a. Personnel;

b. Facility/accommodations;

c. Procedures and method validation;

d. Equipment; and 

e. Standards.

One quality tool that is often used to present the concept of monitoring the entire measurement 

process is a Cause and Effect Diagram where the branches represent the components on this list, 
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examples of measurement assurance methods, and the output represents the results of a 

measurement process.

Figure 1. Cause and effect diagram with measurement assurance perspective.

Please see examples of related measurement assurance resources in Table 1.
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Table 1. Examples of Measurement Assurance Procedures and Tools Available from the NIST and 

the NIST Office of Weights and Measures

Title Description Type of Assessments

NISTIR 6969, SOP 9, 

Control Charts for 

Calibration of Mass 

Standards. (Includes 

spreadsheet job aid.)

This procedure describes procedures 

for the development of control charts 

and their use for demonstrating 

attainment of statistical control of a 

mass calibration process. The 

procedure may be applied to other 

calibration processes as well.

Procedure for: 

• recommended check standards 

for mass calibrations;

• establishing control charts and 

control chart limits;

• monitoring and evaluating 

control chart data;

• monitoring reference values;

• transferring measurement 

statistics for uncertainties; and 

• checklist for evaluation of 

control chart design.

NISTIR 7383, SOP 17, 

Control Charts of 

Laboratory Owned Check 

Standards. (Includes 

spreadsheet job aids.)

This procedure may be used to 

develop and maintain control charts 

to monitor the statistical

control of laboratory check standards 

when replicate measurements are 

made as a part of the standard 

operating procedure. This procedure 

may be used for volume, length, 

time, or other calibrations when 

replicate measurements are made.

Procedure for: 

• establishing control charts and 

control chart limits;

• monitoring and interpretation 

of control chart data; and

• demonstrating example x-bar

and s (standard deviation) 

charts and a data form for 

replicate data.

NISTIR 7383, SOP 20, 

Standard Deviation and 

Range Charts. (Includes 

spreadsheet job aids.)

This procedure describes a process to 

be followed to monitor the statistical 

control of a measurement process 

using standard deviation charts or 

range charts for any calibration

method where replicate 

measurements are performed and 

where it is not practical or feasible to 

maintain laboratory check standards. 

Standard deviation charts are 

preferred to the use of range charts 

for monitoring and evaluation 

process standard deviations when 

replicate measurements are made.

Procedure for: 

• calculating initial statistics;

• creating appropriate charts and 

limits;

• using and interpreting standard 

deviation charts for monitoring 

measurement processes; and

• demonstrating example data 

form for replicate evaluation of 

measurement results.
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Title Description Type of Assessments

NISTIR 6969, SOP 30, 

Process Measurement 

Assurance Program.

The Process Measurement Assurance 

Program (PMAP) is used for the 

control and surveillance of 

measurement performance using 

check standards in measurement and 

calibration procedures. Incorporation 

of these measurement control steps 

ensures the validity of the 

measurement process and the 

standards used. The variables used in 

calculation and assignment of 

uncertainty can be

determined and controlled using this

procedure.

Procedure for:

• modeling the measurement

process;

• selecting and calibrating 

suitable check standards,

• establishing initial statistics,

• creating and preparing charts;

• establishing statistical and 

reference limits;

• evaluating process uncertainty 

components;

• measuring check standards;

• managing and evaluating the 

measurement process;

• using statistical tools for 

ongoing evaluation; and

• instructions on actions.

All measurement SOPs for 

mass, volume, and length.

Calibration procedures published in 

NISTIR 69692, 

NISTIR 56723

, 

NISTIR 73834

, 

And NISTIR 80285.

All Standard Operating Procedures

(SOP) incorporate a section on 

measurement assurance methods 

specific to that calibration 

procedure.

Measurement Assurance 

System Evaluation Form.

Used for laboratory recognition 

and/or accreditation to evaluate 

measurement assurance programs. 

Should be integrated as a part of the 

laboratory Quality Management 

System.

Provides an outline for systematic 

evaluation of a laboratory 

measurement parameter, including 

a series of questions to document a 

periodic assessment. Posted with 

SOP 30. 

PT Follow-Up Form. Originally developed as a form 

associated with NISTIR 7214. Used 

for annual assessment of laboratory 

PT results. Should be integrated as a 

part of the laboratory Quality 

Management System.

Provides a framework for a 

systematic review of proficiency 

testing results. Posted on OWM 

Proficiency Testing website. 

PT Reporting 4-year 

Analysis Form.

Used for laboratory recognition 

and/or accreditation assessments and 

tracking. Should be integrated as a 

part of the laboratory Quality 

Management System. 

Form for tracking laboratory 

results on a rolling 4-year basis 

with plans for the coming year. 

Includes space for tracking 

corrective actions, preventive 

actions, and improvement actions. 

 2 NISTIR 6969, Selected Laboratory and Measurement Practices, and Procedures to Support Basic Mass 

Calibrations, Georgia L. Harris. 3 NISTIR 5672, Advanced Mass Calibrations and Measurements Assurance Program for the State Calibration 

Laboratories, Kenneth L. Fraley, Georgia L. Harris. 4 NISTIR 7383, Selected Procedures for Volumetric Calibrations, Georgia L. Harris. 5 NISTIR 8028, Selected Laboratory and Measurement Practices and Procedures for Length Calibrations, Jose A. 

Torres, Georgia L. Harris.
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Title Description Type of Assessments

Method Validation 

Administrative Procedure

(Sample). Posted with 

OWM State Laboratory 

Resources. 

This sample metrology laboratory 

policy and procedure is used for 

developing and validating test or 

calibration methods when no 

international or national procedures 

are available, when deviating from 

standardized methods, or when no 

standard procedures are available. 

Should be integrated as a part of the 

laboratory Quality Management 

System.

Outlines responsibility and 

authority for method validations 

and approvals; includes:

• procedures for method 

validation;

• types of assessments that 

should be utilized to assure the 

quality of measurement results;

and 

• a sample evaluation form that 

can be used to document the 

assessment of new/laboratory 

procedures;

• use of replicate tests or 

calibrations using the same or 

different methods;

• use and evaluation of check 

standards; and 

• use of interlaboratory 

comparisons. 

NIST IR 69696, Section 8, 

Statistical Techniques. 

Associated with Section 9, 

Reference Tables. 

Includes statistics that are used in 

metrology to summarize 

experimental data, to provide the 

basis for assessing its quality, and to 

provide a basis for making 

probabilistic decisions in its use.

Includes: 

• calculation of standard 

deviations;

• pooling standard deviations,

• estimates of standard deviation 

from range data;

• estimates of within and 

between standard deviation;

• determining confidence and 

statistical tolerance intervals;

• using F-test, t-test, and Welch 

Satterthwaite equation for 

estimating effective degrees of 

freedom; and

• using random numbers. 

 6 NISTIR 6969, Selected Laboratory and Measurement Practices, and Procedures to Support Basic Mass 

Calibrations, Georgia L. Harris. Section 8 was originally part of NIST Handbook 145, Handbook for the Quality 

Assurance of Metrological Measurements, John K. Taylor and Henry V. Oppermann, 1986, which is out of print. 
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Title Description Type of Assessments

NIST/SEMATECH eHandbook of Statistical 

Methods7

Web-based reference that helps

scientists and engineers incorporate 

statistical methods into their work as 

efficiently as possible. Serves as a 

reference on experimental design 

and appropriate data analyses when a 

statistician is not available to help. 

Serves as a useful educational tool to

help users of statistical methods and 

consumers of statistical information 

better understand statistical 

procedures and their underlying 

assumptions, and more clearly 

interpret scientific and engineering 

results stated in statistical terms.

Includes 8 Chapters:

1. Exploratory Data Analysis.

2. Measurement Process

Characterization.

3. Production Process

Characterization.

4. Process Modeling.

5. Process Improvement.

6. Process or Product Monitoring

and Control.

7. Product and Process

Comparisons.

8. Assessing Product Reliability.

7 NIST/SEMATECH e-Handbook of Statistical Methods, http://www.itl.nist.gov/div898/handbook/, January 19, 

2019.