Traceability of a Measurement Result

International vocabulary of metrology-

Basic and general concepts and associated terms (VIM)

JCGM 200:2012(E/F):

2.41 (6.10)
metrological traceability

property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty

1.1 (1.1) quantity

property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference

5.1 (6.1)
measurement standard etalon

realization of the definition of a given quantity, with stated quantity value and associated measurement uncertainty, used as a reference

EXAMPLE 1 1 kg mass measurement standard with an associated standard measurement uncertainty of 3 μg.

220px-Prototype_kilogram_replica.JPG

Replica of the prototype kilogram on display at Cité des Sciences et de l'Industrie in Paris, with protective double glass bell.

Canada, National Research Council  Canada

"Instrument Calibration Policies"

Traceability

Contractual agreements often require that measurements made by contracting laboratories be "traceable" to national and international measurement standards and that the laboratories be able to support these claims of traceability with valid, current documentation and records of the equipment used in the calibration process. Incorrect traceability claims may make a company liable for damages.

The requirement for traceability implies the ability to relate individual measurement results, with a stated uncertainty, through an unbroken chain of comparisons to a stated reference source, usually the Canadian national measurement standards maintained by NRC, or to intrinsic standards based on fundamental natural constants with values assigned or accepted by NRC.

To adequately establish an audit trail outside NRC for purposes of traceability, a calibration result should include: the assigned value, a stated uncertainty, the identity of the standard(s) used in the calibration, and the specification of any environmental conditions of the calibration that require the application of correction factors if the standard or equipment is to be used under different environmental conditions.

NRC supports the practice of making its clients aware of traceability to national measurement standards and providing them with details on how traceability was established.

USA, National Bureau of Standards, NIST, "NIST Quality Manual for
Measurement Services
NIST-QM-I"

6.5 Metrological traceability
6.5.1 NIST adopts for its own use and recommends for use by others the definition of metrological traceability1 provided
in the most recent version of the VIM (see Section 3. Definitions and the NIST traceability site at https://www.nist.gov/nist-policy-traceability).
It is NIST policy to establish traceability of the results of its own measurements and values of its own standards and of
results and values provided to customers of NIST measurement services. Specific evidence of traceability is found in the
NIST sub-level quality documents and other documents referenced therein. Rigorous traceability is a core competency of
NIST.
NIST policy also asserts that providing support for a claim of traceability of the result of a measurement or value of a
standard is the responsibility of the provider — whether NIST or another organization — of that result or value, and that
assessing the validity of such a claim is the responsibility of the user of that result or value. The NIST policy on traceability
is made available to stakeholders on the NIST external website [https://www.nist.gov/nist-policy-traceability].

Magna Carta 1215

•35. Una mensura vini sit per totum regnum nostrum, et una mensura cervisie, et una mensura bladi, scilicet quarterium Londoniense, et una latitudo pannorum tinctorum et russetorum et halbergettorum, scilicet due ulne infra listas; de ponderibus autem sit ut de mensuris.

 

•35. Let there be one measure of wine throughout our whole realm; and one measure of ale; and one measure of corn, to wit, "the London quarter;" and one width of cloth (whether dyed, or russet, or "halberget"), to wit, two ells within the selvages; of weights also let it be as of measures.

Canada, Weights and Measures Act,

R.S.C., 1985, c. W-6

Basis for units of measurement

  • 4 (1) All units of measurement used in Canada shall be determined on the basis of the International System of Units established by the General Conference of Weights and Measures.

Report of the Motherisk Hair Analysis Independent Review

The Honourable Susan E. Lang, Independent Reviewer:

p. 78

"37. It is important to distinguish among research, clinical, and forensic purposes because different standards apply, depending on the manner in which the hair test is intended to be used. Forensic laboratories have the most stringent requirements, including strict chain-of-custody procedures and documentation standards to reduce the risk of contamination of samples and to ensure the traceability and reliability of the results obtained." (italics added)

Footnote 19:

"19 The ISO is an independent, non-governmental member-based organization comprised of 163 national stan-
dards bodies. The ISO is the world’s largest developer of voluntary international standards and has published more
than 19,500 international standards on a variety of subject areas, including standards for laboratories. The ISO does
not accredit laboratories. It promulgates the standards that accrediting bodies use to evaluate laboratories.
20 Though not specific to forensic laboratories, ISO 17025 is recognized internationally as the appropriate standard
for laboratories performing forensic testing. It contains requirements for testing laboratories to demonstrate their
ability to generate valid test results. It consists of 11 tenets and also specific requirements that detail how the tenets
are met, including the assessment of laboratory documentation, the validity and appropriateness of test methods,
proficiency testing, measurement traceability, the technical competence of staff, the testing environment, and mea-
surement uncertainty calculations." (italics added)

Cross-examination of a scientist from the Centre of Forensic Sciences in Toronto:

Q. And above that [CFS 8000C Training Aid December 2013 p. 16 of 238]:

 

"In 1960, the General Conference on Weights and

Measures adopted the International System of

units."

 

With the international abbreviation SI?

A. Yes. Right.

Q. Now, how is it that a measurement result on an

Intoxilyzer 8000C can be traceable to the SI units? Why does

that happen?

A. The instrument is traceable to the standards

that were used to check its calibration.

Q. Really? So you're suggesting that

traceability goes through the control checks by the police

officers, as opposed to the calibration of the instrument by

the factory?

A. No, that's not what I said. It's traceable to

the standards that were used at the point of calibration.

They are the standards obtained from Guth, or another

supplier, who certifies those standards, and the result is

traceable back to those standards.

Q. So on one of the previous days I showed you a

certificate of calibration for this particular Intoxilyzer

8000C that said that the solutions that were used were from a

standard [1828], and you looked at that document, and I think

we may have a copy of it as an exhibit.

A. Yes.

Q. So the traceability of an Intoxilyzer 8000C

goes back through its calibration. Not its control checks,

but through its calibration, right?

A. Correct.

Q. Same if it is recalibrated, the traceability

goes through the standards that are used, the reference

standards. And I think "reference standard" is a technical

term.

A. Yes.

Q. The reference standards that are used at the

time of its recalibration.

A. Correct.

Blog Articles respecting Traceability of a Measurement Result