What is different from an instrument calibration check?
NIST describes uncertainty as information about the dispersion of values attributable to a measured quantity. Its explanation distinguishes standard uncertainty from an interval with a stated coverage probability. Preserve the actual reported quantity and basis rather than give every plus-or-minus number the same meaning.
This worksheet addresses the decision made with a result, not the calibration chain or a unit conversion. Commissioning Docs is independent and is not affiliated with NIST. The worksheet is our administrative review aid, not a NIST acceptance rule.
Sources: NIST: Measurement Uncertainty, updated 17 March 2025
What belongs beside a near-limit reading?
Use the approved procedure and the uncertainty information applicable to this actual measurement. An instrument certificate alone may not describe uncertainty for the complete field method. Leave the result disposition open when the required decision basis is missing.
| Field | Evidence | Review action |
|---|---|---|
| Result | Original value, unit, asset and test event | Preserve the unrounded source |
| Uncertainty | Reported value, unit and meaning | Distinguish standard from expanded uncertainty |
| Coverage basis | Stated factor or probability, when supplied | Do not assume a confidence level |
| Criterion | Exact limit and approved procedure revision | Identify upper, lower or two-sided limit |
| Decision rule | Approved treatment of uncertainty | Request the technical owner if absent |
| Disposition | Reviewer, decision and evidence reference | Do not infer acceptance from the point value |
Why can the point value be insufficient?
Illustrative example. An invented measurement is 9.8 units with a reported interval half-width of 0.4 units. The fictional upper limit is 10.0 units. The interval shown by that report extends from 9.4 to 10.2 units. The point value is below 10.0, while the reported interval crosses it.
That arithmetic does not itself mean pass, fail or a particular probability of compliance. The responsible reviewer must apply the actual approved decision rule and the stated meaning of the interval. Do not silently replace the criterion with 9.6 or disregard the uncertainty to obtain a preferred outcome.
How should an unresolved decision be handed over?
Record the missing rule or uncertainty evidence, assign the technical reviewer and link the affected test record. If a later review changes the disposition, retain the original reading and the reason for the new decision. An open evidence item should not be converted into a passing test by changing rounding or the report date.
The commissioning professional approves the test basis and result disposition. Engineering sign-off is performed only by the registered engineer on the job. This register does not certify equipment or prescribe a field test.
Common questions
What else should the bid team know?
Is a point value below the limit automatically a pass?
Apply the actual approved decision rule and required uncertainty evidence.
Does plus or minus always mean the same confidence level?
No. Preserve the reported uncertainty type and coverage basis.
Should uncertainty be subtracted from a reading to make it pass?
No. Keep the reading intact and use the approved decision rule.