Digit grouping
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.
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 (meaning, 99.95 in decimal point format). This practice derived from the decimal system used in Indian mathematics and was popularized by 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 mark, e.g. 9995. Later, a "separatrix" (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. The separatrix was also used in England as an L-shaped or vertical bar (|) before the popularization of the period and mid dot decimal points.
...
Wikipedia