Calibration, adjustment and verification are different things

The international vocabulary is precise. Calibration establishes the relationship between the instrument's indication and the reference value, with uncertainty. Adjustment is the set of operations that change the instrument so that it indicates correctly. Verification is the provision of objective evidence that the instrument meets specified requirements.

Why it matters

• A calibration certificate with no adjustment still carries the full result; the instrument may be used with corrections.
• Adjusting first and calibrating after destroys the as-found evidence about the previous interval.
• A verification ('within tolerance') is only as good as the decision rule and uncertainty behind it.

Ask for calibration data, then decide on adjustment, then re-calibrate if adjusted. Keep all three records.

Three operations, in the order they belong

The third column is the one that matters commercially. A calibration produces numbers you can use — apply the correction and the instrument is better than it was, with no adjustment at all. A verification produces a verdict, and a verdict is meaningless without a stated decision rule, because a measured error of 0.08 °C against a ± 0.10 °C tolerance with U = 0.05 °C can honestly be reported as a pass or a fail depending on the rule.

The sequence that preserves the evidence

Calibrate first, decide on adjustment second, recalibrate if adjusted. Adjusting first destroys the as-found data, and the as-found data is the only evidence of what the instrument was doing during the interval that just ended — which is exactly what you need if a product decision made three months ago is ever questioned.

A laboratory that adjusts as a matter of routine, without asking, and reports only as-left values has removed that evidence on your behalf. Ask for as-found data explicitly, and ask for it even when no adjustment is made, in which case as-found and as-left are the same and the certificate should say so.

What to ask for, and what to keep

• Ask the laboratory not to adjust without contacting you. The decision belongs to the owner of the measurements the instrument has been making.
• Keep all three records: the as-found calibration, the adjustment if any, and the as-left calibration. Each answers a different question and none substitutes for another.
• An out-of-tolerance as-found result triggers an impact assessment on the measurements made since the previous calibration. That is a nonconforming-work obligation, not an optional courtesy.
• Repeated adjustment at every calibration is a signal, not a service: either the interval is too long or the instrument is not suitable for the tolerance being asked of it.
• Verification without calibration data behind it is an assertion. A sticker saying calibrated with no certificate attached tells you nothing about uncertainty, points, or what pass meant.