Decimal Mark - 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, a tradition derived from the decimal system used in Indian mathematics. Its regular usage and classification can be attributed to the Persian mathematician Al-Khwarizmi, 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 point, e.g. 9995.

Later, a separator (ˌ) (a short, roughly vertical, ink stroke) between the units and tenths position became the norm among Arabic mathematicians. When this character was typeset, it was convenient to use the existing comma (,) or Full stop (.) 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. Many other countries, such as Italy, also chose to use the comma to mark the decimal units position. 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 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 point or mid dot (·), which can also be called an interpunct (often referred to as the decimal point) was preferred for the decimal mark in printing technologies that could accommodate it. This had the advantage of reducing confusion in the countries that used the full stop to separate groups of digits and it was generally clearer in handwriting (particularly when writing on a dotted baseline as on many forms). 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. British aviation magazines thus switched to the US form in the late twentieth century.

When South Africa adopted the metric system, it adopted the comma as its decimal mark, although a number of house styles, including leading newspapers like The Star and The Sunday Times continue to use the decimal point.

The three most spoken international auxiliary languages, Ido, Esperanto, and Interlingua all use the comma as the official radix point, or decimal point. Interlingua has used the comma as its decimal mark since the publication of the Interlingua Grammar in 1951. Esperanto also uses the comma as its official decimal mark, while thousands are separated by non-breaking spaces: 12 345 678,9. 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 point while full stops are used to separate thousands, millions, etc. So the number 12,345,678.90123 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).

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. 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".

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