How to read a calibration certificate
A calibration certificate records evidence of calibration work under the stated conditions. Start by checking that it describes the correct instrument and the work you need. A familiar logo or a recent issue date is not enough to make every result suitable for your use.
Start with identity and coverage
Use these questions when reviewing a document:
| Detail | Question to ask |
|---|---|
| Laboratory and certificate reference | Who issued it, and can this exact document be identified? |
| Instrument identity | Do the serial number, asset reference and description match your equipment? |
| Calibration and issue dates | When was the work performed, and when was the report issued? These may differ. |
| Method, range and test points | Was the required work actually covered? |
| Conditions and limitations | Are there restrictions on how the results may be used? |
| Results and units | Are the values indications, errors or corrections, and which units apply? |
| Uncertainty statement | Which uncertainty is reported, with what coverage factor or probability? |
| Conformity statement, if present | Which specification and decision rule support the conclusion? |
These are reading prompts, not an exhaustive certificate template. Reporting requirements and terminology are explained in UKAS LAB 5: Reporting calibration results.
Understand one result row
In this fictional example, a reference value is 100.00 °C, the instrument indicates 100.30 °C, and the reported error is +0.30 °C. If the certificate reports expanded uncertainty of 0.10 °C, that uncertainty describes the measurement of the result. It is not a second error to subtract from the reading.
Check the document's definitions before applying corrections. The calibration and traceability guide explains error signs; the uncertainty guide explains coverage factors.
As found commonly describes the condition before adjustment or repair; as left describes it afterwards. Read any qualifying notes. A satisfactory as-left result does not remove the need to assess how an unacceptable as-found condition may have affected earlier work.
Read accreditation and pass/fail claims separately
Check which results the accreditation claim covers and whether the laboratory's scope fits the quantity, range, method and location involved. The scope guide explains those boundaries.
Calibration results can be reported without a pass/fail statement. Where a statement is present, read the specification and rule behind it. The decision-rule guide explains why the same measured value may lead to different outcomes under different rules.
Keep the evidence connected in Metra
Attach an external certificate to the correct calibration event. Check its identity and contents before relying on it, and retain earlier versions when a replacement is issued. A stored file does not automatically approve the event.
For Metra-generated certificates, use the verification reference to check the published status and any replacement. A superseded or voided certificate needs review; opening its PDF does not restore it to current status.
Metra tracks the next due date through the equipment's calibration requirement. Do not treat the certificate's issue date as a universal expiry date. Confirm that the requirement reflects the work and interval your organisation has established.