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The International System of Units ((フランス語:Système International d'Unités), SI) is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units. It defines twenty-two named units, and includes many more unnamed coherent derived units. The system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative that started in 1948. It is based on the metre-kilogram-second system of units (MKS) rather than any variant of the centimetre–gram–second system (CGS). SI is intended to be an evolving system, so prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves. The 25th General Conference on Weights and Measures (CGPM) in 2014, for example, discussed a proposal to change the definition of the kilogram. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems and the lack of coordination between the various disciplines that used them. The CGPM, which was established by the Metre Convention of 1875, brought together many international organisations to not only agree on the definitions and standards of the new system but also agree rules on writing and presenting measurements in a standardised manner around the world. The International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. While metrication in the United States is consistent in science, medicine, government, and various fields of technology and engineering, common measurements are mostly performed in United States customary units, although these have officially been defined in terms of SI units. The United Kingdom has officially adopted a policy of partial metrication, with no intention of replacing imperial units immediately. Canada has adopted the SI for most governmental, medical and scientific purposes and for such varied uses as grocery weights, weather reports, traffic signs and gasoline sales, but imperial units are still legally permitted and remain in common use throughout many sectors of Canadian society, particularly in the building trade and the railway sector. ==History== (詳細はmetric system was first implemented during the French Revolution (1790s) with just the metre and kilogram as standards of length and mass〔 The differences between "weight" and "mass" were only formally qualified in 1901.〕 respectively. In the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. The inclusion of electrical units into the system was hampered by the customary use of more than one set of units, until 1900 when Giovanni Giorgi identified the need to define one single electrical quantity as a fourth base quantity alongside the original three base quantities. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram and metre against agreed prototypes from French to international control. In 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. In 1948, an overhaul of the metric system was set in motion which resulted in the development of the "Practical system of units" which, on its publication in 1960, was given the name "The International System of Units". In 1954, the 10th General Conference on Weights and Measures (CGPM) identified electric current as the fourth base quantity in the practical system of units and added two more base quantities—temperature and luminous intensity—making six base quantities in all. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin and candela. In 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「International System of Units」の詳細全文を読む スポンサード リンク
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