Three different operations
Calibration establishes a relationship between instrument indications and reference values, with their uncertainties. Verification checks whether defined requirements are met. Adjustment changes the instrument’s response. They are not synonyms: an instrument may be calibrated yet show a deviation making it unsuitable for a particular measurement.
Related concept: Industrial hygiene.
What a certificate provides
A certificate gives results, corrections and uncertainties under specified conditions. It must correspond to the identified instrument and the range or quantity of interest. A dated sticker does not replace that information. Traceability requires a documented relationship to appropriate references; comparison with another instrument alone does not establish it.
Deciding whether the instrument is suitable
Before use, compare performance with the method’s requirements and the decision to be made. Range, resolution, stability and environmental conditions matter. Calibration at points far from the intended use may not meet the need. Acceptance criteria must be set beforehand, not invented after seeing the result.
The programme and field checks
The programme identifies instruments requiring control, who performs it, frequency, method and records. Intervals account for use, history, consequences of error and applicable instructions or requirements. Checks before and after a measurement campaign may detect drift or damage; they do not automatically replace full calibration or mandatory legal verification.
If an instrument fails
Prevent unauthorised use and assess the effect on previous measurements. For example, a deviation discovered at the end of a shift may require reviewing affected samples and repeating part of the work. Replacing the sticker or adjusting the instrument without retaining the initial result conceals information needed for that assessment.
Example and scope
In a hypothetical example, a detector responds to test gas, but the check verifies only a defined response; it does not demonstrate accuracy for every gas and concentration. The record must state what was actually checked. For instruments subject to metrological control, calibration and statutory verification have different effects; the programme must address both where applicable.
