5. A few words about accuracy

Measurement uncertainties are not limited to random effects. Systematic (or rather "predictable") effects can also mar measurement results.

In general, these effects are sought in measuring instruments during calibration. Calibration consists in comparing a result given by the instrument under near-ideal conditions with the result it should give "in theory". Calibration involves measuring known objects (standards) and recording the deviation. In the case of "measuring" instruments (versus materialized standards), several calibration points are sampled over the measurement range. In theory, this first phase of the calibration process should be completed by a second, as stipulated by the VIM in its new definition of the calibration operation: