Decimal mark

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For the proper choice of the decimal mark in English language Wikipedia articles, see Wikipedia:Manual of Style (dates and numbers)#Decimal points.
"Decimal period" redirects here. For the length of the repeating sequence in the decimal expansion of a rational number, see Repeating decimal.

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.

History[edit]

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. 9995. This practice derived from the decimal system used in Indian mathematics[1] and was popularized by the Persian mathematician Al-Khwarizmi,[2] 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 (a short, roughly vertical, ink stroke) between the units and tenths position became the norm among Arab mathematicians, e.g. 99ˌ95. 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.[3]

In France, the full stop was already in use in printing to make Roman numerals more readable,[how?] so the comma was chosen.[citation needed] Many other countries, such as Italy, also chose to use the comma to mark the decimal units position.[4] 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 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.[5] 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 20th century.

When South Africa adopted the metric system, it adopted the comma as its decimal mark,[6] 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 official radix point, or decimal point. Interlingua has used the comma as its decimal mark since the publication of the Interlingua Grammar in 1951.[7] 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 (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).[8]

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.[9] 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".[10] This usage has therefore been recommended by technical organizations, such as the United States' National Institute of Standards and Technology.

Digit grouping[edit]

For ease of reading, numbers with many digits may be divided into groups using a delimiter.[11] In some countries, these "digit group separators" are only employed to the left of the decimal mark; in others, they are also used to separate long decimal numbers as well.

The groups created by the delimiters tend to follow the use of the local language, which varies. In European languages, large numbers are read in groups of thousands and the delimiter (which occurs every three digits when it is used) may be called a "thousands separator". In East Asian cultures, particularly China, Japan, and Korea, large numbers are read in groups of myriads (10,000s) and the delimiter accordingly separates every four digits.[citation needed] The Indian numbering system is somewhat more complex: it groups the rightmost three digits in a similar manner to European languages but then groups every two digits thereafter: 1.5 million would accordingly be written 15,00,000 and read as "15 lakh".[citation needed]

The convention for digit group separators varies but usually seeks to distinguish the delimiter from the decimal mark. Typically, English-speaking countries employ commas as the delimiter—10,000—and other European countries employ periods or spaces: 10.000 or 10 000. Because of the confusion that can result in international documents, the withdrawn SI/ISO 31-0 standard advocates the use of spaces[12] and the International Bureau of Weights and Measures and International Union of Pure and Applied Chemistry advocate the use of a "thin space" in "groups of three".[13][14] Within the United States, the American Medical Association's widely-followed AMA Manual of Style also calls for a thin space.[11] In some online encoding environments (for example, ASCII-only) a thin space is not practical/available, in which case a regular word space or no delimiter are the alternatives. The Metrication Board proposed this system for the United Kingdom and, while it is not universally adopted, it is standard within the country's construction industry.

In some programming languages, it is possible to group the digits in the program's source code to make it easier to read. Ada, D, Java, Perl and Ruby use the underscore (_) character for this purpose. All these languages allow writing seven hundred million as 700_000_000. C++14 allows the use of the apostrophe (') for digit grouping and therefore seven hundred million can be represented as 700'000'000.

Exceptions to digit grouping[edit]

The International Bureau of Weights and Measures states that "when there are only four digits before or after the decimal marker, it is customary not to use a space to isolate a single digit".[13] Likewise, some manuals of style state that thousands separators should not be used in normal text for numbers from 1000 to 9999 inclusive where no decimal fractional part is shown (in other words, for four-digit whole numbers), whereas others use thousands separators, and others use both. For example, APA style stipulates a thousands separator for "most figures of 1,000 or more" except for page numbers, binary digits, temperatures, etc.

There are always common-sense exceptions to digit grouping, such as years, postal codes and ID numbers of predefined nongrouped format, which style guides usually point out.

In non-base-10 numbering systems[edit]

In binary (base-2), a full space can be used between groups of four digits. Similarly, in hexadecimal (base-16), full spaces are usually used to group digits into twos.

Influence of calculators and computers[edit]

In countries with a decimal comma, the decimal point is also common as the "international" notation because of the influence of devices, such as electronic calculators, which use the decimal point. Most computer operating systems allow selection of the decimal mark and programs that have been carefully internationalized will follow this, but some programs ignore it and a few are even broken by it.[which?]

Hindu–Arabic numeral system[edit]

Decimal marks:[citation needed]
Point "." – Blue
Comma "," – Green
Eastern Arabic numerals – Red
Data unavailable – Grey

Countries using Arabic numerals with decimal point[edit]

Countries where a dot "." is used to mark the radix point comprise roughly 60% of the world's population.[citation needed] They include:[citation needed]

Australia, Botswana, British West Indies, Brunei, Canada (when using English), Dominican Republic, Egypt, Guatemala, Honduras, Hong Kong, India, Ireland, Israel, Japan, Kenya, Korea (both North and South), Lebanon, Luxembourg (uses both marks officially), Macau (in Chinese and English text), Malaysia, Malta, Mexico, Mongolia, Nepal, New Zealand, Nicaragua, Nigeria, Pakistan, Panama, People's Republic of China, Philippines, Singapore, Sri Lanka, Switzerland, Taiwan, Tanzania, Thailand, Uganda, United Kingdom, United States (including insular areas), Zimbabwe.

Countries using Arabic numerals with decimal comma[edit]

Countries where a comma "," is used to mark the radix point comprise roughly 24% of the world's population.[citation needed] They include:[citation needed]

Albania, Andorra, Angola, Argentina, Armenia, Austria, Azerbaijan, Belarus, Belgium, Bolivia, Bosnia and Herzegovina, Brazil, Bulgaria, Cameroon, Canada (when using French), Chile, Colombia, Costa Rica, Croatia (comma used officially, but both forms are in use), Cuba, Cyprus, Czech Republic, Denmark, East Timor, Ecuador, Estonia, Faroes, Finland, France, Germany, Georgia, Greece, Greenland, Hungary, Iceland, Indonesia, Italy, Kazakhstan, Kirgistan, Latvia, Lebanon, Lithuania, Luxembourg (uses both marks officially), Macau (in Portuguese text), Macedonia, Moldova, Mongolia, Morocco, Mozambique, Netherlands, Norway, Paraguay, Peru, Poland, Portugal, Romania, Russia, Serbia, Slovakia, Slovenia, South Africa, Spain, Switzerland, Sweden, Tunisia, Turkey, Ukraine, Uruguay, Uzbekistan, Venezuela, Vietnam.

Other numeral systems[edit]

Unicode defines a decimal separator key symbol (⎖ in hex U+2396, decimal 9110) which looks similar to the apostrophe. This symbol is from ISO/IEC 9995 and is intended for use on a keyboard to indicate a key that performs decimal separation.

In the Arab world, where Eastern Arabic numerals are used for writing numbers, a different character is used to separate the integer and fractional parts of numbers. It is referred to as an Arabic decimal separator (٫) in Unicode. An Arabic thousands separator (٬) also exists.

In Persian, the decimal mark is called momayyez, which is written like a forward slash—there is a small difference between the "comma" character used in sentences and the momayyez (٫) used to separate sequences of three digits. To separate sequences of three digits, a comma or blank space may be used; however this is not a standard.[15][16][17]

In English Braille, the decimal point, , is distinct from both the comma, , and the period / full stop .

Examples of use[edit]

The following examples show the decimal mark and the thousands separator in various countries that use the Hindu–Arabic numeral system.

Style Countries
1234567,89 SI style (French version), Albania, Austria, Belgium, Bosnia, Brazil, Bulgaria, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Italy, Latin Europe, Lithuania, Netherlands (non-currency numbers, see below), Poland, Portugal, Romania, Russia, Serbia, Slovakia, Slovenia, South Africa, Spain, Sweden
1234567.89 SI style (English version), Australia, Canada, China
1,234,567.89 China, Ireland, Israel, Japan, Korea, Malaysia, Mexico, New Zealand, Philippines, Singapore, Taiwan, Thailand, United Kingdom, United States
1,234,567·89 Ireland, Japan, Korea, Malaysia, New Zealand, Philippines, Singapore, Taiwan, Thailand, United Kingdom, United States (older, typically hand written)
1.234.567,89 Austria, Brazil, Denmark, Germany, Greece, Indonesia, Italy, Netherlands (currency), Portugal, Romania, Russia, Slovenia, Spain (older),[18] Sweden (not recommended)
1˙234˙567,89 Italy (handwriting)
12,34,567.89 India (see Indian Numbering System)
1'234'567.89 Switzerland (printed, computing, currency, international requisite, everyday use)
1'234'567,89 Switzerland (handwriting)
1.234.567'89 Spain (handwriting)
123,4567.89 China (alternative), Japan (alternative)
  • In Albania, Belgium, Bosnia, Estonia, France, Hungary, Poland, Slovakia and much of Latin Europe as well as French Canada: 1234567,89 (In Spain, in handwriting it is also common to use an upper comma: 1.234.567'89)[citation needed]
  • In Brazil, Denmark, Germany, Greece, Indonesia, Italy, Netherlands, Portugal, Romania, Russia, Slovenia, Sweden and much of Europe: 1234567,89 or 1.234.567,89. In handwriting, 1˙234˙567,89 is also seen, but never in Brazil, Denmark, Germany, the Netherlands, Portugal, Romania, Russia, Slovenia or Sweden. In Italy a straight apostrophe is also used in handwriting: 1'234'567,89. In the Netherlands, the points thousands separator is preferred in currency amounts, and the space for other large numbers[citation needed].
  • In Germany and Austria, thousands separators were often denoted by alternating uses of comma and point, e.g. 1.234,567.890,12[19][20] for "one billion 234 million ..."
  • In Switzerland: There are two cases. 1'234'567.89 is used for currency values. An apostrophe as thousands separator along with a "." as decimal symbol. For other values the SI style 1234567,89 is used with a "," as decimal symbol. The apostrophe is also the most common variety for non-currency values: 1'234'567,89, though this usage is officially discouraged.
  • In Ireland, Israel, Japan, Korea (both), Malaysia, New Zealand, the Philippines, Singapore, Taiwan, Thailand, the United Kingdom, and the United States: 1,234,567.89 or 1,234,567·89; the latter is generally found only in older, and especially handwritten, documents. Australia used this style up until the 1970s; now it uses the SI style.[21]
  • In English Canada: There are two cases. The preferred method for currency values is $4,000.00 while for numeric values it is 1234567.89; however, commas are also sometimes used although no longer taught in school or used in official publications.[22]
  • SI style: 1 234 567.89 or 1 234 567,89 (in their own publications the dot is used in the English version and the comma in the French version).
  • In China, comma and space are used to mark digit groups because dot is used as decimal mark. There is no universal convention on digit grouping, so both thousands grouping and no digit grouping can be found. However, grouping can also be done every four digits: 123,4567.89, since names for large numbers in Chinese are based on powers of 10,000 (e.g. the next new word is for 108). Japan is similar, although when grouping by myriads numeral kanji are frequently used as separators: 1億2345万6789.
  • In South Asia, due to a numeral system using lakhs (lacs) (1,23,456 equal to 123 456) and crores (1,23,45,678 equal to 12 345 678), comma is used at levels of thousand, lakh and crore, for example, 10 million (1 crore) would be written as 1,00,00,000.
South Asian Value Value
One 1
Ten 10
Hundred 100
Thousand 1,000
Lakh 100,000
Crore 10,000,000
Arab 1,000,000,000
Kharab 100,000,000,000

Unicode characters[edit]

Used with Western Arabic numerals (0123456789):

  • U+0020   space
  • U+0027 ' apostrophe
  • U+002C , comma
  • U+002E . full stop
  • U+00B7 · middle dot
  • U+02D9 ˙ dot above

Used with Eastern Arabic numerals (٠١٢٣٤٥٦٧٨٩):

  • U+066B ٫ arabic decimal separator
  • U+066C ٬ arabic thousands separator

Used with keyboards:

  • U+2396 decimal separator key symbol (resembles an apostrophe)

See also[edit]

References[edit]

  1. ^ 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.
  2. ^ Khwarizmi, Abu Jafar Muhammad ibn Musa al-, Oxford Islamic Studies Online
  3. ^ Devlin, Keith (2011). The Man of Numbers: Fibonacci's Arithmetic Revolution. New York: Walker & Company. pp. 44–45. ISBN 9780802779083. 
  4. ^ 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."
  5. ^ 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.
  6. ^ Government Notice R. 1144, Government Gazette 4326, 5 July 1974
  7. ^ Grammar of Interlingua: Parts of Speech – Numerals
  8. ^ Gramat Volapüka. Cathair na Mart: Evertype. ISBN 978-1-904808-94-7
  9. ^ Perlis, Alan, The American Side of the Development of ALGOL, ACM SIGPLAN Notices, August 1978.
  10. ^ [1], Resolution 10.
  11. ^ a b Iverson, Cheryl, et al. (eds) (2007). AMA Manual of Style (10th ed.). Oxford, Oxfordshire: Oxford University Press. p. 793. ISBN 978-0-19-517633-9. 
  12. ^ "Decimals Score a Point on International Standards". 2006-11-22. Retrieved 2008-11-27. 
  13. ^ a b International Bureau of Weights and Measures. "Rules and style conventions for expressing values of quantities": "Formatting numbers and the decimal marker".
  14. ^ "Guidelines for drafting IUPAC technical reports and recommendations". 2007. Retrieved 2008-11-27. 
  15. ^ Pournader, Roozbeh (2000-10-15). "Persian decimal separator". Unicode Mail List Archive. Unicode Consortium. Retrieved 2008-06-21. 
  16. ^ "The Decimal Numeral". Academic Grammar of New Persian. Archived from the original on 2006-06-20. Retrieved 2006-06-19. 
  17. ^ Descriptive Grammar of New Persian (archived)
  18. ^ Diccionario panhispánico de dudas, when writing numbers more than four figures, these three will be grouped into three, starting from the right, and separating the groups by whitespace. (Exceptions: Never written with periods, commas or white separation numbers that refer to years, pages, verses, urban roads, postal codes, legal articles, decrees or laws.)
  19. ^ Röll. "Enzyklopädie des Eisenbahnwesens". Retrieved 26 August 2014. , entry "Union Pacific-Eisenbahn", largest numbers in table
  20. ^ Röll. "Enzyklopädie des Eisenbahnwesens". Retrieved 26 August 2014. , entry "Bilanz", sums in last table
  21. ^ Steinle, Vicki. "Teaching and Learning about Decimals". Retrieved 20 April 2012. 
  22. ^ Government of Canada (2011-01-13). "Public Service Commission Style Guide". Retrieved 2013-09-25.