1. Understanding the challenges of periodic calibration/verification

It's an indisputable fact that all measuring and testing equipment drifts over time, for a wide variety of reasons. In mechanical engineering, or more precisely in dimensional measurement, a steel gauge block may become thinner through wear and tear following frequent use; in electricity, the indication of a voltmeter may vary slowly or abruptly following the ageing of a resistor in the voltmeter's input circuit. As a result of this drift, the measuring instrument may indicate erroneous measurement values. The instrument's maximum permissible error (MPE), indicated in a test procedure for example, may no longer be respected. Products measured with this instrument could then be declared as not conforming to a specification, even though they do conform, or vice versa!

To avoid this deterioration in risk, the metrological characteristics of the instrument need to be...