CALIBRATIONS BY COMPARISON IN METROLOGY - A SURVEY

Comparison calibrations (CCs) are important in metrology, as usually h igh-precision measurements are performed by comparison to a known refe rence with the use of a comparator, that is, of an instrument capable of accurately measuring differences or ratios, which are small to the values of the measurand. This is, for example, the case of mechanical quantities, such as mass and volume, and of electrical quantities, suc h as voltage, capacity, resistance and frequency. The paper examines t he mathematical aspects of CCs, with particular attention to recent de velopments in time and mass metrology.