Calibration and Verification

Calibration determines the relationship between an instrument indication and reference values under stated conditions. Verification checks whether the instrument or measurement system satisfies defined acceptance requirements. Adjustment may follow either activity, but it is not the same as calibration.

The required range, resolution, tolerance and uncertainty should be selected around the process decision. A display with many decimal places can still be unsuitable when its uncertainty is large relative to the limit being controlled.

Before-use checks, routine verification and formal calibration intervals should reflect instrument stability, frequency of use, handling, environment, previous results and the consequence of error. One universal calendar interval is not defensible for every device.

Reference weights, buffers, thermometric points and other standards must be identified, within status and appropriate to the working range. Temperature, equilibration, contamination and sample preparation can affect the comparison.

When an instrument fails acceptance, control is not restored merely by adjusting or replacing it. The operation must assess which earlier measurements and product decisions may have been affected, then document disposition and corrective action.

Records should connect instrument identity, location or use, reference standard, result, uncertainty or tolerance, action, reviewer and next due status. The objective is a defensible measurement decision, not a certificate detached from production use.