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A foot ( feet; abbreviation: ft; symbol: ′, the prime symbol) is a unit of length in the imperial and US customary systems of measurement. Since 1959, both units have been defined by international agreement as equivalent to 0.3048 meters exactly. In both systems, the foot comprises 12 inches and three feet compose a yard. Historically the "foot" was a part of many local systems of units, including the Greek, Roman, Chinese, French, and English systems. It varied in length from country to country, from city to city, and sometimes from trade to trade. Its length was usually between 250 mm and 335 mm and was generally, but not always, subdivided into 12 inches or 16 digits. The United States is the only industrialized nation that uses the international foot and the survey foot (a customary unit of length) in preference to the meter in its commercial, engineering, and standards activities. The foot is legally recognized in the United Kingdom; road signs ''must'' use imperial units, while its usage is widespread among the British public as a measurement of height.〔Alder, Ken (2002). The Measure of all Things—The Seven-Year-Odyssey that Transformed the World. London: Abacus.〕 The foot is recognized as an alternative expression of length in Canada〔''(Weights and Measures Act ), accessed January 2012, Act current to 2012-01-18. Basis for units of measurement 4.(1) All units of measurement used in Canada shall be determined on the basis of the International System of Units established by the General Conference of Weights and Measures. (...) Canadian units (5) The Canadian units of measurement are as set out and defined in Schedule II, and the symbols and abbreviations therefore are as added pursuant to subparagraph 6(1)(b)(ii).〕 officially defined as a unit derived from the meter〔''(Weights and Measures Act )''〕 although both have partially metricated their units of measurement. The measurement of altitude in the aviation industry is one of the few areas where the foot is widely used outside the English-speaking world. ==Historical origin== Historically the human body has been used to provide the basis for units of length. The foot of a white male is typically about 15.3% of his height, giving a person of 160 cm () a foot of 245 mm and one of 180 cm () a foot of 275 mm. These figures are less than the foot used in most cities over time, suggesting that the "foot" was actually a synonym for a "shoe". Archeologists believe that the Egyptians and Mesopotamians preferred the cubit while the Romans and the Greeks preferred the foot. Under the Harappan linear measures, Indus cities during the Bronze Age used a foot of 13.2 inches (333.5 mm) and a cubit of 20.8 inches (528.3 mm).〔Kenoyer JM (2010) "Measuring the Harappan world," in Morley I & Renfrew C (edd) The Archaeology of Measurement, 117; http://a.harappa.com/sites/g/files/g65461/f/Kenoyer%202010%20Measuring%20the%20Harappan%20World.pdf〕 The Greek foot (ποὐς, ''pous'') had a length of of a stadion,〔(History of Herodotus : a new English version, book II, 6.7 )〕 one stadion being about 181.2 m,〔http://www.perseus.tufts.edu/hopper/artifact?name=Epidauros%2C+Stadium&object=Building〕 therefore a foot being at the time about 302 mm. Its exact size varied from city to city and could range as much as between 270 mm and 350 mm, but lengths used for temple construction appear to have been about 295 mm to 325 mm, the former being close to the size of the Roman foot. The standard Roman foot (''pes'') was normally about 295.7 mm (97% of today's measurement), but in the provinces, the ''pes Drusianus'' (foot of Nero Claudius Drusus) was used, with a length of about 334 mm. (In reality, this foot predated Drusus.) Originally both the Greeks and the Romans subdivided the foot into 16 digits, but in later years, the Romans also subdivided the foot into 12 ''unciae'' (from which both the English words "inch" and "ounce" are derived). After the fall of the Roman Empire, some Roman traditions were continued but others fell into disuse. In AD 790 Charlemagne attempted to reform the units of measure in his domains. His units of length were based on the ''toise'' and in particular the ''toise de l'Écritoire'', the distance between the fingertips of the outstretched arms of a man. The ''toise'' has 6 ''pied'' (feet) each of 326.6 mm (12.86 in). He was unsuccessful in introducing a standard unit of length throughout his realm: an analysis of the measurements of Charlieu Abbey shows that during the 9th century the Roman foot of 296.1 mm was used; when it was rebuilt in the 10th century, a foot of about 320 mm〔The original reference was given in a round number of centimeters〕 was used. At the same time, monastic buildings used the Carolingian foot of 340 mm.〔 The procedure for verification of the foot as described in the 16th century by Jacob Koebel in his book ''Geometrei. Von künstlichem Feldmessen und absehen'' is: 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「Foot (unit)」の詳細全文を読む スポンサード リンク
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