Comparable measurement
Measurement standards are needed to make measurement results comparable. In early history emperors, kings and other rulers ordered that certain measurement standards had to be used all over their empire. References were spread over the empire, which materialized the foot, inch, barrel or pound to be used. These measurement standards mostly differed from the ones used in other states. Only in 1875 a worldwide treaty, the Meter Convention was closed, in order to achieve an international system of standards.

Definition of a standard
The metrological vocabulary VIM defines a measurement standard as: a material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit or one or more values of a quantity to serve as a reference. See also terms in metrology.

Examples
Well-known examples of modern measurement standards are the platinum-iridium kilogram for mass, the Caesium 133 atomic clock for time and frequency, the Josephson junction for voltage. More and more measurement standards are related to universal constants of nature, like the velocity of light, the electronic charge and the constant of Planck.

Accessibility and traceability
It is very important that a citizen, industry, company, institute or other organization have access to those measurement standards that are relevant to their work. For this purpose most states have established one or more national standards laboratories. For the Netherlands this is NMi Van Swinden Laboratory that offers a wide range of services. Calibration laboratories play an important role in the further distribution of standards to provide traceability of measurement results. The international comparability is established by an intensive cooperation in various international metrological organizations.