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A decimal mark is a symbol used to separate the integer part from the fractional part of a number written in decimal form. Different countries officially designate different symbols for the decimal mark. The choice of symbol for the decimal mark also affects the choice of symbol for the thousands separator used in digit grouping, so the latter is also treated in this article. In mathematics the decimal mark is a type of radix point, a term that also applies to number systems with bases other than ten. Conversationally, the decimal point is commonly referred to as a "decimal dot." ==History== In the Middle Ages, before printing, a bar ( ¯ ) over the units digit was used to separate the integral part of a number from its fractional part, e.g. 995 (meaning, 99.95 in decimal point format). This practice derived from the decimal system used in Indian mathematics〔Reimer, L., and Reimer, W. ''Mathematicians Are People, Too: Stories from the Lives of Great Mathematicians, Vol. 2''. 1995. pp. 22-22. Parsippany, NJ: Pearson Education, Inc. as Dale Seymor Publications. ISBN 0-86651-823-1.〕 and was popularized by the Persian mathematician Al-Khwarizmi,〔(Khwarizmi, Abu Jafar Muhammad ibn Musa al- ), Oxford Islamic Studies Online〕 when Latin translation of his work on the Indian numerals introduced the decimal positional number system to the Western world. His ''Compendious Book on Calculation by Completion and Balancing'' presented the first systematic solution of linear and quadratic equations in Arabic. A similar notation remains in common use as an underbar to superscript digits, especially for monetary values without a decimal mark, e.g. 9995. Later, a separator (a short, roughly vertical, ink stroke) between the units and tenths position became the norm among Arab mathematicians, e.g. 99(unicode:ˌ)95. When this character was typeset, it was convenient to use the existing comma (99,95) or full stop (99.95) instead. Gerbert of Aurillac marked triples of columns with an arc (called a "Pythagorean arc") when using his Hindu–Arabic numeral-based abacus in the 10th century. Fibonacci followed this convention when writing numbers such as in his influential work ''Liber Abaci'' in the 13th century. In France, the full stop was already in use in printing to make Roman numerals more readable, so the comma was chosen.〔Enciclopedia Universal Santillana, 1996 by SANTILLANA S.A., Barcelona, Spain. ISBN 84-294-5129-3. Comma, def.2: "coma: MAT. Signo utilizado en los números no enteros para separar la parte entera de la parte decimal o fraccionaria; p.ej., 2,123."〕 Many other countries, such as Italy, also chose to use the comma to mark the decimal units position.〔Enciclopedia Universal Santillana, 1996 by SANTILLANA S.A., Barcelona, Spain. ISBN 84-294-5129-3. Comma, def.2: "coma: MAT. Signo utilizado en los números no enteros para separar la parte entera de la parte decimal o fraccionaria; p.ej., 2,123."〕 It has been made standard by the ISO for international blueprints. However, English-speaking countries took the comma to separate sequences of three digits. In some countries, a raised dot or dash (') may be used for grouping or decimal mark (see examples below); this is particularly common in handwriting. In the United States, the full stop or period (.) was used as the standard decimal mark. In the nations of the British Empire, although the full stop could be used in typewritten material and its use was not banned, the interpunct (also known as the decimal point, point, or mid-dot) was preferred for the decimal mark in printing technologies that could accommodate it, e.g. 99·95.〔Reimer, L., and Reimer, W. ''Mathematicians Are People, Too: Stories from the Lives of Great Mathematicians, Vol. 1''. 1990 p. 41. Parsippany, NJ: Pearson Education, Inc. as Dale Seymor Publications. ISBN 0-86651-509-7.〕 However, as the mid-dot was already in common use in the mathematics world to indicate multiplication, the SI rejected its use as the decimal mark. During the beginning of British metrication in the late 1960s, and with impending currency decimalisation, there was widespread debate in the United Kingdom as to whether the decimal comma or decimal point should be preferred; the British Standards Institution and some sectors of industry advocated the comma, and the Decimal Currency Board advocated for the point. In the event, the point was decided on by the Ministry of Technology in 1968. When South Africa adopted the metric system, it adopted the comma as its decimal mark,〔Government Notice R. 1144, ''Government Gazette'' 4326, 5 July 1974〕 although a number of house styles, including some English-language newspapers, such as ''The Sunday Times'' continue to use the full stop. The three most spoken international auxiliary languages, Ido, Esperanto, and Interlingua all use the comma as the decimal mark. Interlingua has used the comma as its decimal mark since the publication of the Interlingua Grammar in 1951.〔(Grammar of Interlingua: Parts of Speech – Numerals )〕 Esperanto also uses the comma as its official decimal mark, while thousands are separated by non-breaking spaces: . Ido's ''Kompleta Gramatiko Detaloza di la Linguo Internaciona Ido'' (Complete Detailed Grammar of the International Language Ido) officially states that commas are used for the decimal mark while full stops are used to separate thousands, millions, etc. So the number 12,345,678.90123 (in American notation) for instance, would be written ''12.345.678,90123'' in Ido. The 1931 grammar of Volapük by Arie de Jong uses the comma as its decimal mark, and (somewhat unusually) uses the middle dot as the thousands separator (12·345·678,90123).〔(Gramat Volapüka. Cathair na Mart: Evertype. ISBN 978-1-904808-94-7 )〕 In 1958, disputes between European and American delegates over the correct representation of the decimal mark nearly stalled the development of the ALGOL computer programming language.〔Perlis, Alan, ''The American Side of the Development of ALGOL'', ACM SIGPLAN Notices, August 1978.〕 ALGOL ended up allowing different decimal marks, but most computer languages and standard data formats (e.g. C, Java, Fortran, Cascading Style Sheets (CSS)) specify a dot. The 22nd General Conference on Weights and Measures declared in 2003 that "the symbol for the decimal marker shall be either the point on the line or the comma on the line". It further reaffirmed that "numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups"〔(), Resolution 10.〕 e.g. 1 000 000 000. This usage has therefore been recommended by technical organizations, such as the United States' National Institute of Standards and Technology. 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「Decimal mark」の詳細全文を読む スポンサード リンク
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