Decimal separator

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The decimal separator is a symbol used to mark the boundary between the integral and the fractional parts of a decimal numeral.

1 History
2 Examples of use
3 Dot countries
4 Comma countries
5 Momayyez countries
6 See also

[edit] 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. However, its regular usage and classification is attributed to Muhammad ibn Musa al-Khwarizmi, a Persian scientist. Later, a separator (a short, roughly vertical, ink stroke) between the units and tenths position became the norm. When this character was typeset, it was convenient to use the existing comma (,) or period (.) instead.

In France, the period was already in use in printing to make Roman numerals more readable, so the comma was chosen. Many other countries 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 U.S., the period (.), which is called a "stop" or "full stop" in most other countries, was used as the standard decimal separator. In the nations of the British Empire, although the period could be used in typewritten material, the point (middle dot: ·), which can also be called an interpunct, was preferred for the decimal separator in technologies that could accommodate it. This had the advantage of reducing confusion in the countries that used the period 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 middle dot was already in common use in the mathematics world to indicate multiplication, the SI rejected this use of the middle dot as the decimal separator. However, the use of the period as decimal point was not banned. 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 separator. The constructed language Esperanto uses the comma as its official decimal separator.

In the Arab world and Iran, where Arabic digits are used for writing numbers, a different character called momayyez — which is written like a forward slash — is used to separate the integer and fractional parts of numbers. To separate sequences of three digits, a comma or blank space may be used; however, this is not a standard. In Persian, there is a small difference between the "comma" character used in sentences and the comma-like character used to separate sequences of three digits.[1]

The separator in non-decimal numeral systems may be referred to as a radix point.

[edit] Examples of use

The following is ordered chronologically, by when each country adopted the use:

In France, Finland, and much of Latin Europe: 1 234 567,89
In Germany, the Netherlands, Belgium, Italy, Romania and much of Europe: 1 234 567,89 or 1.234.567,89 (in handwriting you may also come across 1^·234^·567,89)
In Switzerland (mainly German-speaking Switzerland): 1'234'567,89
In the United Kingdom, United States, Japan, and Mexico: 1,234,567.89 or 1,234,567·89; the latter is more commonly found in older, and especially handwritten, documents nowadays; many UK schools now teach the SI style, which has become official in Australia.
SI style: 1 234 567.89 (dot countries) or 1 234 567,89 (comma countries)
In China, the comma is sometimes used to separate blocks of four digits: 123,4567.89, since in Chinese, there is a word for 10,000 (the next new word is for 10⁸, not 10⁶ as in most languages).
In India, due to a numeral system using lakhs (100,000) and crores (10,000,000), an asymmetric distribution of comma separators is often used, for example, 30 million (3 crores) would be written as 3,00,00,000, with commas at the thousand, lakh, and crore levels.

In countries with a decimal comma, the decimal point is also common as the "international" notation and under the influence of e.g. electronic calculators using the decimal point. Computer programs can usually be adapted to use the local separator, but even on the same computer it is not uncommon that some programs use commas and some use points.

Note: notations like "12,345", "12.345", "12,345.678", and "12.345,678" are ambiguous by a factor of 1000 if the notational system is not known.