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What is the correct way to refer to NIST?

#1
Good day.
What is the correct way to refer to NIST? Is it sufficient to state that xxx measuring equipment has been calibrated using NIST? or should we expect to have a procedure number after NIST?
Thanks in advance.
 
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Marc

Captain Nice
Staff member
Admin
#2
You need to cite something specific such as a NIST procedure (or procedures) or specific NIST requirements.

"...using NIST..." isn't specific enough in your internal documents. It is too vague.
 

Sidney Vianna

Post Responsibly
Staff member
Admin
#3
Good day.
What is the correct way to refer to NIST? Is it sufficient to state that xxx measuring equipment has been calibrated using NIST? or should we expect to have a procedure number after NIST?
Thanks in advance.
Are you trying to ask if, in your calibration certificate, there should be traceability information that allows full traceability to a NIST standard? Your question, as is, is not clearly formulated.
 
#4
First, in answer to your question, here is what NIST says about referencing their "number":

" I.B.4 Is a NIST Test Report Number necessary and/or sufficient evidence of traceability?
Test report numbers issued by NIST are intended to be used solely for administrative purposes. Although they are often used to uniquely identify documents which bear evidence of traceability, test report numbers themselves do not address the issues listed in I.B.1 above, and should not be used nor required as the sole proof of traceability. "

This means that just because someone produces a "NIST number" on their certificate this is not proof by itself that the measurement is traceable.


So, in memory of Bob Pease, "What's all this Traceability Stuff, Anyhow?"

First question. What does a calibration certificate prove? That the equipment calibrated is in tolerance, accurate.
Great. But what does that really mean? And what is the NIST reference about?

Back in the not so good old days when you bought and sold items you had to trust that the merchant was using "honest" weights. In time it was decided that the government needed to step in and assure that a pound in London weighed the same as a pound in Boston. That set up the establishment of the BIPM, the international organization based in France that held the "golden" standards of weights and measures, also known as the SI units. They made duplicates of these standards and distributed them to member countries. In the United States those are held by NIST (OK purists, I know that these are no longer physical artifacts, but let's agree to simplify things for this lesson). This is why you see that things are "Traceable to NIST" - that means that we can compare our results to ones produced at NIST, so everyone compares to the same standard. That means you should get the same results everywhere.

So what does this mean for calibrations?
The requirement is "The laboratory shall ensure that measurement results are traceable to the International System of Units (SI)..."
You do that through a process of Metrological Traceability:

Establishing metrological traceability
Metrological traceability is established by considering, and then ensuring, the following:
a) the specification of the measurand (quantity to be measured);
b) a documented unbroken chain of calibrations going back to stated and appropriate references
(appropriate references include national or international standards, and intrinsic standards);
c) that measurement uncertainty for each step in the traceability chain is evaluated according to
agreed methods;
d) that each step of the chain is performed in accordance with appropriate methods, with the
measurement results and with associated, recorded measurement uncertainties;
e) that the laboratories performing one or more steps in the chain supply evidence for their technical
competence.

So the "appropriate references" referred to here are the "Traceable to NIST" statements you see on calibration certificates. That does not mean that the item was calibrated at NIST, just that you can trace the measurements directly back to NIST. Also, NIST is only one of many National Laboratories who are BIPM members, so Canada has their NRC, Great Britain the NPL, Germany the PTB, etc. That's why many calibration certificates refer to "NIST or other National Laboratory" in their traceability statements.
 
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