# Measurand

According to DIN 1319 on the “Basics of Measurement Technology ”, the **measured variable is** the physical variable to which a measurement applies. In this standard, the term is used both for “measured variable in the general sense” and for “special measured variable”.

- In the general sense it is a physical quantity such as B. mass , power , temperature , the target of a measurement was or will be. Delimitation: Since z. For example, if the intelligence quotient is not a physical quantity, it cannot be a measurable quantity in the sense of this definition.
- A special size is a size belonging to special benefits in kind, such as B. Volume of a submitted body, resistance of a submitted copper wire at a given temperature. The value of a special measurand supplied or to be supplied by a measuring device or a measuring device is called the
*measured value*; it is expressed by the product of the numerical value and the unit of measurement . Delimitation: For the purposes of this definition, values that e.g. B. were obtained by mere consideration or assumption, not to be referred to as measured values.

The measured variable does not have to be the subject of the measurement directly. It can also be determined using physically known or fixed mathematical relationships from quantities to which direct measurements apply. The aim of every measurement is to determine the *true value of* the measurand. At best, however, it is possible to provide an estimated value by means of a *complete measurement result* .

The measurand is often a property of a body such as length or mass. It can also be a property of a process, such as the speed of movement or the wavelength of radiation , or a state, such as the field strength of an electric field .

Each measured variable has a dimension in the underlying size system , so that values of the measured variable are usually to be compared with other values of the same dimension. This comparability is expressed by specifying the value of a measured variable as a multiple of the associated unit of measurement . Some measured quantities are quantities of the dimension number (e.g. angle , refractive index , eccentricity of the orbit of a satellite, etc.) whose values can be obtained directly as rational numbers . In practice, auxiliary units of measurement are often used for these quantities too, which are only used for the sake of clarity.

In the field of quantum physics , certain measured quantities of one and the same system are *complementary* to one another, i. That is, the measurement of one quantity has the effect that the value of the other quantity becomes completely indefinite (see quantum mechanics or observables ).