Should Calibration Certificates include NIST Traceability numbers?

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During late 2017, I was performing an AS 9100 audit in the US where my team mate observed calibration certificates lacking “NIST Traceability Numbers”. NIST is the US “National Institute of Standards and Technology” (equivalent to NPL, the UK’s National Metrology Institute). He informed me that he had a “Major Nonconformity”. To his amazement, I informed him that there is no such thing as “NIST Traceability Numbers”. He insisted otherwise… informing me that, as an Aerospace auditor with over 30 years experience, he had been trained to always verify metrological traceability through “NIST Traceability Numbers”. And no one had ever questioned this.

I explained to him that what he is referring to are actually the NIST “Test Numbers”, which are used by NIST for administrative purposes only. This is supported by official documents from NIST, which he insisted that I show him.

NIST GMP 13, “Good Measurement Practice for Ensuring Metrological Traceability”, sec. 1.1 (3rd para.) states:
Test numbers issued by NIST should not be used nor required as proof of the adequacy or traceability of a test or measurement. Having a NIST number does not provide evidence that the measurement value provided by another organization has the property of metrological traceability.


NIST GMP 13, “Good Measurement Practice for Ensuring Metrological Traceability”, sec. 1.6.3, “Use of, or reference to, official test numbers of a national metrology institute” states:
Having an authentic test number does not provide assurance or evidence that the measurement value provided by another organization is traceable. Not only must there be an unbroken chain of comparisons, but each measurement must be accompanied by a statement of uncertainty associated with the value. Test report numbers should not be used nor required as proof of the adequacy or traceability of a test or measurement. National and international documentary standards for test and measurement quality requirements, such as ISO 10012, ISO/IEC 17025 and the ISO 9000 series, provide guidance for assessing metrological traceability and do not require the use or reporting of specific test numbers to establish metrological traceability.

Questions about verifying calibration certificates iso 9001So how should we verify metrological traceability (to satisfy ISO 9001 & AS9100, sec.

The key lies in ISO 9001 & AS9100, sec. 8.4.1, which requires the organization to “determine and apply criteria for the evaluation, selection, monitoring of performance, and re-evaluation of external providers, based on their ability to provide processes or products and services in accordance with requirements.”

While NIST GMP 13, “Good Measurement Practice for Ensuring Metrological Traceability”, sec. 1.5, defines the seven essential elements necessary to ensure metrological traceability, the easiest way to ensure metrological traceability is to require all calibration service providers (metrology laboratories) to be ANSI/ASQ Z540 and/or ISO 17025 accredited by an accreditation body that is recognized as a signatory of the “International Laboratory Accreditation Cooperation” (ILAC) “Mutual Recognition Agreement” (MRA). A searchable listing of all ILAC MRA signatory bodies is available online.

All of our Calibration Certificates state traceability “to international or national measurement standards”. Why isn’t that good enough?

Even though your calibration certificates contain a statement of metrological traceability, you must verify the validity of those statements in order to conform with ISO 9001 & AS9100, sec. & 8.4.1.

We’ve been using the same Calibration Laboratory for years…  so we “Grandfathered” them to be an approved supplier (on the basis of past performance). Isn’t that good enough?

No. By stating that you’ve “grandfathered” a calibration service provider (on the basis of past “perceived” past performance), you’re admitting to the auditor that you’ve not bothered to verify metrological traceability as a part of the “evaluation” and “selection” criteria.

We typically send our instruments to the OEM for calibration (i.e., Metrological Confirmation). Isn’t that good enough?

While many OEMs (Original Equipment Manufacturers) of measuring equipment are experts who should  know what they’re doing, this isn’t always the case. Some OEMs cut corners… and fail to maintain metrological traceability. Any OEM of measuring instrumentation who doesn’t maintain a ANSI/ASQ Z540 and/or ISO 17025 accredited metrology laboratory, should be considered “suspect”.

iso 9001 calibration certificatesThan why have ISO 9001 auditors been accepting these Calibration Certificates?

Unfortunately, poor training. If you’ve read this far, you now know more than the vast majority of auditors about metrological traceability.

ISO 9000:2015, “Quality management systems — Fundamentals and vocabulary”, sec. 3.6.13 “traceability”, includes:
Note 2 to entry: In the field of metrology, the definition in ISO/IEC Guide 99 is the accepted definition.

ISO/IEC Guide 99 is simply a re-packaged and re-numbered version of the free BIPM JCGM 200, “International vocabulary of metrology – Basic and general concepts and associated terms (VIM)”. And it defines “metrological traceability” (in sec. 2.41) as:
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.

Therefore, if you’ve not been verifying the “documented unbroken chain of  calibrations” from your calibration service providers , as “evaluation” and “selection” criteria, then you’ve not adequately ensured metrological traceability.

What should you do?

Eventually, you may encounter an auditor who has read the documents referenced above and/or been properly trained in these requirements. And if that happens, in order to avoid a nonconformance, you should ensure that you’re only using ANSI/ASQ Z540 and/or ISO 17025 accredited metrology labs.

To learn more about Rick Randall, click here.

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