Decimal separator
[6][2][7] In some specialized contexts, the word decimal is instead used for this purpose (such as in International Civil Aviation Organization-regulated air traffic control communications).
In mathematics, the decimal separator is a type of radix point, a term that also applies to number systems with bases other than ten.
A similar notation remains in common use as an underbar to superscript digits, especially for monetary values without a decimal separator, as in 9995.
Positional decimal fractions appear for the first time in a book by the Arab mathematician Abu'l-Hasan al-Uqlidisi written in the 10th century.
His Compendious Book on Calculation by Completion and Balancing presented the first systematic solution of linear and quadratic equations in Arabic.
[12] The earliest known record of using the decimal point is in the astronomical tables compiled by the Italian merchant and mathematician Giovanni Bianchini in the 1440s.
[13][contradictory] Tables of logarithms prepared by John Napier in 1614 and 1619 used the period (full stop) as the decimal separator, which was then adopted by Henry Briggs in his influential 17th century work.
In some countries, a raised dot or dash (upper comma) may be used for grouping or decimal separator; this is particularly common in handwriting.
The three most spoken international auxiliary languages, Ido, Esperanto, and Interlingua, all use the comma as the decimal separator.
[22] In 1958, disputes between European and American delegates over the correct representation of the decimal separator nearly stalled the development of the ALGOL computer programming language.
[23] ALGOL ended up allowing different decimal separators, 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[26] declared in 2003, “The symbol for the decimal marker shall be either the point on the line or the comma on the line.” It further reaffirmed, (1 000 000 000 for example).
[27] Past versions of ISO 8601, but not the 2019 revision, also stipulated normative notation based on SI conventions, adding that the comma is preferred over the full stop.
[28] ISO 80000-1 stipulates, “The decimal sign is either a comma or a point on the line.” The standard does not stipulate any preference, observing that usage will depend on customary usage in the language concerned, but adds a note that as per ISO/IEC directives, all ISO standards should use the comma as the decimal marker.
An important reason for grouping is that it allows rapid judgement of the number of digits, via telling at a glance ("subitizing") rather than counting (contrast, for example, 100 000 000 with 100000000 for one hundred million).
The use of thin spaces as separators,[30]: 133 not dots or commas (for example: 20 000 and 1 000 000 for "twenty thousand" and "one million"), has been official policy of the International Bureau of Weights and Measures since 1948 (and reaffirmed in 2003) stating as well as of the International Union of Pure and Applied Chemistry (IUPAC),[31][32] the American Medical Association's widely followed AMA Manual of Style, and the UK Metrication Board, among others.
In East Asian cultures, particularly China, Japan, and Korea, large numbers are read in groups of myriads (10 000s) but the delimiter commonly separates every three digits.
[31][32] Within the United States, the American Medical Association's widely followed AMA Manual of Style also calls for a thin space.
Common examples include spreadsheets and databases in which currency values are entered without such marks but are displayed with them inserted.
It is useful because the number can be copied and pasted into calculators (including a web browser's omnibox) and parsed by the computer as-is (i.e., without the user manually purging the extraneous characters).
Java, JavaScript, Swift, Julia, and free-form Fortran 90 use the underscore (_) character for this purpose; as such, these languages allow seven hundred million to be entered as 700_000_000.
For example, APA style stipulates a thousands separator for "most figures of 1000 or more" except for page numbers, binary digits, temperatures, etc.
