Metrology is the scientific study of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in France when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure conformity between the countries, the Bureau International des Poids et Mesures (BIPM) was established by the Metre Convention. This has evolved into the International System of Units (SI) as a result of a resolution at the 11th General Conference on Weights and Measures (CGPM) in 1960.
Metrology is divided into three basic overlapping activities:
- The definition of units of measurement
- The realisation of these units of measurement in practice
- Traceability—linking measurements made in practice to the reference standards
These overlapping activities are used in varying degrees by the three basic sub-fields of metrology:
- Scientific or fundamental metrology, concerned with the establishment of units of measurement
- Applied, technical or industrial metrology—the application of measurement to manufacturing and other processes in society
- Legal metrology, covering the regulation and statutory requirements for measuring instruments and methods of measurement
In each country, a national measurement system (NMS) exists as a network of laboratories, calibration facilities and accreditation bodies which implement and maintain its metrology infrastructure. The NMS affects how measurements are made in a country and their recognition by the international community, which has a wide-ranging impact in its society (including economics, energy, environment, health, manufacturing, industry and consumer confidence). The effects of metrology on trade and economy are some of the easiest-observed societal impacts. To facilitate fair trade, there must be an agreed-upon system of measurement.