On May 20, 1875, 17 different countries signed the Treaty of the Meter (also called the Meter Convention) to establish new international prototypes for mass and length. In addition to defining the official unit of mass as the kilogram (kg), the Treaty of the Meter also created three international organizations to oversee the new standards:
- CGPM, Conférence générale des poids et mesures) — a diplomatic organization that makes decisions about international standards. This is the group that voted on the revised SI in November 2018.
- The International Committee on Weights and Measures (CIPM, Comité international des poids et mesures) — comprises 18 people, each from a different nation that has signed the Treaty of the Meter. Makes recommendations and submits draft resolutions to the General Conference.
- The International Office of Weights and Measures (BIPM, Bureau international des poids et mesures) — an intergovernmental organization with headquarters near Paris. It operates under the supervision of the International Committee and has custody of the International Prototype Kilogram (IPK), the former official standard by which masses were measured.
The International System (SI)
The International System of Units (SI, short for Le système international d'unités) was established under that name in 1960 and now includes seven base units for seven quantities:
- meter (length)
- kilogram (mass)
- second (time)
- ampere (electric current)
- kelvin (thermodynamic temperature)
- mole (amount of substance)
- candela (luminous intensity)
Other quantities, such as energy, power, pressure and magnetic flux, can be derived from these seven. Explore the chart below to see how these units are related.