Evaluate and quantify the drift of a measuring instrument

The question of drift in measuring instruments is an essential one in metrology. Calibration establishes the "metrological state" of the instrument on the date it is carried out, but what does it tell us about tomorrow, a month from now, or at the end of the calibration validity period? If, with certain instrumentation (in particular "fixed" instruments, for instance "physical" standards and limit gauges) the situation is relatively straightforward, it is not so simple with instruments that take measurements. The FD X 07-014[1] booklet, moreover, distinguishes between the two types of device, those where drift can be observed (since calibration uncertainties tend to be minor, which is generally true of size standards) and the others (measuring instruments). This article deals with the specific case of measuring.