STANDARD

The standard is an object, an instrument or a reference value used to adjust and check — to calibrate — devices and Measuring instruments. It embodies a unit or a quantity with a known accuracy, against which routine measurements are compared to ensure their correctness. The hierarchy of standards, from the International Bureau of Weights and Measures to national laboratories and then to workshops, ensures the traceability of measurements. In horology, a discipline devoted to the measurement of Time, the concept of the standard is central: the instruments for Testing the rate, the dimensional gauges and the time bases are periodically checked against reference standards. Historically, high-precision timepieces — marine chronometers, clocks with Pendulum — have themselves served as time standards. The modern definition of the second is now based on atomic clocks, the ultimate frequency standards, on which all contemporary time metrology depends.