While the term metrology refers to measurement techniques in general, it is used more specifically to mean the study of techniques to measure classical quantities. Metrology is concerned with how to make measurements as accurately as possible, and to quantify how accurate a measurement technique is. Precise measurements of quantities such as frequency and mass are important for establishing and maintaining standard units. Other effectively classical quantities that one may wish to measure are acceleration and the strengths of magnetic or electric fields.

Metrology is concerned not only with measurements of single fixed quantities but also with quantities that vary in time, usually called signals or waveforms. Since all signals have some maximum rate at which they change, they can be discretized by sampling with sufficient frequency. Thus all signals can be regarded as finite sets of values to be measured. Nevertheless, the fact that these values arrive in a sequence with a given duration places practical limitations on their measurement. Optimal methods for measuring signals are important in communication, and in many scientific applications where data is time-varying and noisy.