A measurement is a comparison between a measurand and a reference quantity representing a physical unit. The quantity to be measured is unknown and is displayed during the measurement as a quantitative measured value together with the corresponding physical unit. For example, 102 volts or 0.334 mA.
The reference quantity is a calibrated quantity derived from a measurement standard. The displayed measured value depends on various influences, which are expressed in the measurement inaccuracy, and can deviate from the actual measured quantity.
For electrical and electronic measurements, a distinction can be made between continuous and discontinuous, indirect and direct, and between analog and digital measurements. Furthermore between static and dynamic measurements.
Continuous measurement is a continuous measurement in which the measured values are displayed without interruption. Strictly speaking, such a continuous measurement can only be measured with analog displaying measuring instruments or screen measuring instruments. Every digital measurement, on the other hand, is a discontinuous measurement in which the measured variable is sampled and digitized at periodic or aperiodic intervals. Between the individual samples there is always a period of time during which the measurand is undetermined.
Indirect measurement is an indirect measurement in which the measured value is represented by an indirect calculation from other measured quantities. In contrast, a direct measurement is based on a direct comparison with a reference standard.
In static measurement, the measurand does not change over time. The transient response of the measurand must have decayed before the static measurement is performed using a known measurement principle.
On the other hand, in dynamic measurement, a measurand is measured that changes over time. The measuring principle and the display of the measurand must be appropriate to the changing measurand. A typical measuring instrument for dynamic measurements is the oscilloscope.
The differentiation of metrological precision and accuracy is ensured by counting, testing, calibration, adjustment and calibration, which are reflected in the characteristics of the measurement samples, the reference reference and certification.