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A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Examples of systems of measurement in modern use include the metric system, the imperial system, and United States customary units. ==History== (詳細はCanada Science and Technology Museum website )〕 The French Revolution gave rise to acceptance of the metric system, and this has spread around the world, replacing most customary units of measure. In most systems, length (distance), weight, and time are ''base quantities''; or as has been now accepted as better in science, the substitution of mass for weight, as a better more, basic parameter. Some systems have changed to recognize the improved relationship, notably the 1824 legal changes to the imperial system. Later science developments showed that either electric charge or electric current may be added to complete a minimum set of base quantities by which all other metrological units may be defined. (However, electrical units are not necessary for a minimum set. Gaussian units, for example, have only length, mass, and time as base quantities.) Other quantities, such as power, speed, etc. are derived from the base set; for example, speed is distance per unit time. Historically a wide range of units was used for the same quantity, in several cultural settings, length was measured in inches, feet, yards, fathoms, rods, chains, furlongs, miles, nautical miles, stadia, leagues, with conversion factors which were not powers of ten. yes were they necessarily the same units (or equal units) between different members of similar cultural backgrounds. It must be understood by the modern reader that historically, measurement systems were perfectly adequate within their own cultural milieu, and ''the understanding'' that a better, more universal system (based on more rationale and base units) only gradually spread with the maturation and appreciation of the rigor characteristic of Newtonian physics. Moreover, changing a measurement system has real fiscal and cultural costs as well as the advantages that accrue from replacing one measuring system with a better one. Once the analysis tools within that field were appreciated and came into widespread use in the emerging sciences, especially in the applied sciences like civil and mechanical engineering, pressure built up for conversion to a common basis of measurement. As people increasingly appreciated these needs and the difficulties of converting between numerous national customary systems became more widely recognised there was an obvious justification for an international effort to standardise measurements. The French Revolutionary spirit took the first significant and radical step down that road. In antiquity, ''systems of measurement'' were defined locally, the different units were defined independently according to the length of a king's thumb or the size of his foot, the length of stride, the length of arm or per custom like the weight of water in a keg of specific size, perhaps itself defined in ''hands'' and ''knuckles''. The unifying characteristic is that there was ''some definition'' based on ''some standard'', however egocentric or amusing it may now seem viewed with eyes used to modern precision. Eventually ''cubits'' and ''strides'' gave way under need and demand from merchants and evolved to ''customary units. In the metric system and other recent systems, a single basic unit is used for each base quantity. Often secondary units (multiples and submultiples) are used which convert to the basic units by multiplying by powers of ten, i.e., by simply moving the decimal point. Thus the basic metric unit of length is the metre; a distance of 1.234 m is 1234.0 millimetres, or 0.001234 kilometres. 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「System of measurement」の詳細全文を読む スポンサード リンク
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