International System of Units
The International System of Units is a system of units of measurement built from i seven base units, ii a collection of derived units, and iii a collection of prefixes used to form both binary and decimal multiples and submultiples of units.
The International System of Units is universally abbreviated SI, a term that derives from the French
Le Système International d'Unités. The SI is the modern form of the metric system. The metric system was conceived by a group of scientists –leaded by , the
father of modern chemistry– who had been commissioned by the Assemblée nationale and of France to create a unified and rational system of measures. On 10 December 1799, the metric system was definitively adopted in France.
The SI was established in 1960 by the 11th General Conference on Weights and Measures (CGPM) –Conférence Générale des Poids et Mesures–. The CGPM is the international authority that ensures wide dissemination of the SI and modifies the SI as necessary to reflect the latest advances in science and technology. The CGPM was created by the Metre Convention –Convention du Mètre–, a treaty signed in Paris in 1875 with the desire for international cooperation on metrology.
The SI is declared as an evolving system, thus prefixes and units definitions are created and modified through international agreement as the technology of measurement progresses, and as the precision of measurements improves. The SI is universally used in science and has become the dominant language of international commerce and trade 1.
The SI is defined to be a coherent system of units –i.e., the system verifies that each derived unit has a proportionality factor of one with regard to the base units– 2,3. However, the use of the SI prefixes destroys this coherence 2.
The current version of the SI suffers from other deficiencies and ambiguities. However, it is the best system available at the time of writing this, and the advantages of using an international system of units compensates its minor deficiencies. It is waited that the SI will be improved in future versions.
References and notes
- Only three nations have not officially adopted the SI as their primary or sole system of measurement: Myanmar (Burma), Liberia, and the United States.
- Quantities, Units and Symbols in Physical Chemistry, IUPAC Green Book, 3rd Ed., 2nd Printing 2008: IUPAC & RSC Publishing; Cambridge.
- International Vocabulary of Metrology, Basic and General Concepts and Associated Terms (VIM), 3rd ed. 2008: Joint Committee for Guides in Metrology (JCGM). .
Date: 2013 January 03, 20:23:44+01:00