Metrology is 'the science of measurement'. It covers both the theoretical and the practical issues related to measurement. The aim of measurement is to determine the value of a quantity, for instance length, temperature, time, electrical resistance or the amount of substance of a certain material. Several basic elements need to be available to carry out an accurate measurement. First of all measurement standards are needed, by which the measurement equipment to be used, can be calibrated. The measurement has to proceed according to a specified protocol.
The assessment of (inter)nationally agreed measurement methods is the work of the Nederlandse Normalisatie Instituut NEN. Measurements carried out by law occupy an special position.

Measurement Standards
For example the platinum-iridium kilogram or the Caesium 133 atomic clock .

Measuring instruments and their characteristics
Such as measurement systems in production and control processes.

Measurements
Including the methods of measurement, estimation of uncertainty and deviation, and environmental effects.

Legal metrology
The part of metrology that relates to statutory requirements and legislation.