A product is gauged against a national reference standard, such as the «primary kilogram». Originally, this was kept as a platinum-iridium cylinder in a vault in Paris until 2019. Now, the kilogram - as well as the meter - is derived from a natural constant: The exact value of the kilogram, for example, will in future be derived from Planck´s constant. It links the amount of energy of a light wave with its frequency and always has the same value. Via its unit of measurement [kg m2/s], Planck´s constant is clearly related to kilogram - and thus also to meter and second.
Gauging is a test prescribed by law for the compliance of a test equipment with the prescribed measured values according to the Weights and Measures Act. Gauging may only be carried out by public authorities, the gauging offices. Furthermore, only measuring instruments whose design has been certified as calibratable in an approval procedure can be gauged. In general, the Weights and Measures Act was introduced to protect the consumer: All measuring instruments, of which the result is converted into a monetary value for the customer, are subject to obligatory gauging. This also includes deadweight testers.