Decimal Mark - Digit Grouping

Digit Grouping

For ease of reading, numbers with many digits before or after the decimal mark may be divided into groups using a delimiter, with the counting of groups starting from the decimal mark in both directions. This delimiter is usually called a thousands separator, because the digits are usually in groups of three, that is, thousands. The most general name for this delimiter is digit group separator, because thousands are not always the relevant group. For example, in various countries (e.g., China, India, and Japan), there have been traditional conventions of grouping by 2 or 4 digits. These conventions are still observed in some contexts, although the 3-digit group convention is also well known and often used. Making groups of three digits also emphasizes that there is a base 1000 of the numeral system that is being used, which is not always a given (for example, in computer science).

As with the decimal mark, there have been several common conventions for which character to use for the digit group separator. If the decimal mark is a point, the digit group separator is often a comma or a space. If the decimal mark is a comma, the digit group separator is often a point or a space. The problem with the point and the comma as either decimal mark or digit group separator is that, internationally, they have both often been used for both meanings, and their meaning is context-dependent (one must know which notational system is being used in order to interpret them). Therefore the space is recommended in the SI/ISO 31-0 standard, and the International Bureau of Weights and Measures states that "for numbers with many digits the digits may be divided into groups of three by a thin space, in order to facilitate reading. Neither dots nor commas are inserted in the spaces between groups of three". Other style-defining bodies are also moving toward this clearer notation. For example, the International Union of Pure and Applied Chemistry (IUPAC) suggest never using a comma or a point as thousands separator: "For numbers with many digits, the digits may be separated in groups of three, counting from the decimal sign toward the left and the right. The groups should be separated by a thin space (half space), and never by a comma or a point, or by any other means." The American Medical Association, whose AMA Manual of Style is widely followed in health professions literature, also endorses a space for digit group separator. (Specifically, a thin space is endorsed for typesetting; a regular word space is sufficient wherever typographical nicety is impractical.) The United Kingdom Metrication Board also proposed this system for Metrication in the United Kingdom and, while not universally adopted, it is the standard in the UK construction industry.