Traceability is a property of the measurement result, not a badge on the instrument. And the military standard that many specifications still cite was cancelled long ago.
- ✓ VIM definition: documented, unbroken chain of calibrations
- ✓ NIST does not certify the traceability of measurements it does not itself perform
- ✓ MIL-STD-45662A, Rev. A of 1988: cancelled
- ✓ Current references: ANSI/NCSL Z540-1 (then Z540.3), ISO 10012, ISO/IEC 17025
Calibration certificates often carry the phrase “NIST traceable”, and specifications just as often refer to MIL-STD-45662A. Both expressions deserve checking, because neither today means what those who write them usually intend.
Let us start from the definition. According to the VIM, the international vocabulary of metrology, metrological traceability is the “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”: the “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”.
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NIST itself is explicit on two points. The first: “NIST does not define, specify, assure, or certify metrological traceability of the results of measurements except those that NIST itself provides”, that is, “NIST does not define, specify, assure, or certify metrological traceability of the results of measurements except those that NIST itself provides”. The second: “traceability is the property of the result of a measurement, not of an instrument or calibration report or laboratory”, that is, “traceability is the property of the result of a measurement, not of an instrument or calibration report or laboratory”.
MIL-STD-45662A: what happened
| Item | Item |
|---|---|
| Document | MILITARY STANDARD: CALIBRATION SYSTEM REQUIREMENTS, DoD |
| Revision | Rev. A, 1 August 1988 |
| Status | Cancelled, marked as superseded by ISO 10012-1 and ANSI Z540-1 |
| Date of supersession | Indication of 20 January 1995, reported by a single source |
| Current references | ANSI/NCSL Z540-1 (then Z540.3), ISO 10012, ISO/IEC 17025 |
What to write in a specification today
We think it right to say it plainly: MIL-STD-45662A is cancelled. Revision A is dated 1 August 1988 and is marked as superseded by ISO 10012-1 and ANSI Z540-1; the indication of supersession on 20 January 1995 comes from a single source and we report it as such, not as an established fact. Continuing to cite it in a purchase specification means requiring conformity to a document that is no longer in force.
The current references for calibration systems are ANSI/NCSL Z540-1 and the subsequent Z540.3, ISO 10012 and, for the competence of testing and calibration laboratories, ISO/IEC 17025. These are the ones to refer to when writing a new requirement.
As for the wording “NIST traceable”, the practical consequence of the two statements quoted above is simple: what makes a certificate defensible is not the name of an institute printed on the cover, but the documented chain of calibrations and the stated uncertainty. Our service is described on the Calibration and setting page.
Recommended instruments
| Item | Use |
|---|---|
| Calibration blocks | Physical reference for verifying the measurement chain |
| Precision transducers | Probes used in high-accuracy verifications |
| DakMaster | Data management and production of the measurement documentation |
| Dakota PMX2-DL | Universal precision gauge with data logger |
Frequently asked questions
No. Revision A, dated 1 August 1988, is cancelled and marked as superseded by ISO 10012-1 and ANSI Z540-1. There is also an indication of supersession on 20 January 1995, which we report as coming from a single source.
The current references for calibration systems: ANSI/NCSL Z540-1 and the subsequent Z540.3, ISO 10012 and, for the competence of testing and calibration laboratories, ISO/IEC 17025.
NIST states that it does not define, specify, assure or certify the metrological traceability of measurement results other than those it provides itself, and makes clear that traceability is a property of the result of a measurement, not of an instrument, a calibration report or a laboratory.
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