Almost every calibration certificate says NIST-traceable. It is one of the first things a CLIA or CAP surveyor looks for, and one of the least understood. Here is what it means and how to tell whether a certificate really backs it up.
The short answer
A measurement is NIST-traceable when it can be linked, through an unbroken chain of calibrations, to the standards kept by the National Institute of Standards and Technology. Your pipette was checked on a balance; the balance was calibrated with reference weights; those weights were calibrated against higher-level standards; and so on up to NIST. Each link in the chain has a documented result and a stated uncertainty.
NIST does not calibrate or certify your equipment directly. Traceability is about the chain, not about NIST touching your instrument.
What a traceable certificate should show
- The instrument: make, model and serial or asset number
- The reference standard used, with its ID and its own calibration due date
- The measurement uncertainty
- As-found results before any adjustment, and as-left results after
- The test points and the tolerance they were judged against
- Date, technician and next due date
A certificate that just says "NIST-traceable" with a pass stamp, and nothing about the reference used or its due date, is the kind a surveyor may question.
Traceable vs. ISO 17025 accredited
These are different things. Traceability describes the chain of measurements. ISO/IEC 17025 accreditation means an independent body, such as A2LA, has audited a calibration lab's methods, competence and quality system. An accredited lab's calibrations are traceable, but a traceable calibration is not always from an accredited lab. Some labs and contracts require accredited calibrations; most clinical labs need traceable ones with good documentation.
BMCA's reference standards are themselves calibrated by an A2LA-accredited laboratory, so every measurement on our certificates has an unbroken traceability chain.
Why it matters for your lab
Surveyors are not checking the word on the certificate. They are checking that you can prove your results were measured with instruments that were verified against something reliable, and when. A complete, traceable certificate does that in one page.
See our lab equipment calibration services, or read how to choose a calibration service.