Writing of numbers

Decimal separator/decimal mark

The decimal separator can be either a full stop or a comma. Commas are more noticeable, as they are larger and extend below the baseline. In addition, a comma marks a pause or break, whereas a full stop usually indicates an end. This logic also makes the comma more suitable as decimal mark. Most European languages use the comma as decimal separator. Modern international standards allow either character as the decimal mark (U+002C Comma; U+002E Full stop).

Digit group separator/thousands separator

Numbers with many digits before or after the decimal mark are often divided into groups, using a delimiter. This makes reading and understanding numbers much easier, as all European languages use a positional notation system based on the number 1 000 for spoken numbers. Additionally, this works nicely with the prefixes of our measuring system, such as milli-, kilo, mega-, etc., which are also based on the number 1 000. That’s why long numbers are usually arranged into groups of three digits, both before and after the decimal mark (for example 1 234 567 890,123 45).

Historical practice employed many different characters as digit group separators, for example full stops, commas and apostrophes. This caused misunderstandings in international communication, especially as some of these characters were also used as decimal mark. Modern international standards recommend a thin space, which avoids any confusion, and is language-independent. This solution also works with both decimal markers, comma and full stop. Good typography uses this digit group separator for long numbers, out of courtesy to the reader, for the sake of clarity and well-balanced visual impression.

The best space to use for this purpose is U+202F Narrow no-break space. This also guarantees that the number is not split at automated line breaks. If the narrow no-break space is not available, U+00A0 No-break space, U+0020 Space or omitting the digit group separator altogether can be alternatives.

Negative numbers/minus sign

Standard computer keyboards provide only one centred horizontal line character, the U+002D Hyphen-minus. Unfortunately, this hybrid character has to be a compromise in design. The typographically correct minus sign has the same length and position as the vertical bar of the plus sign and has the character code U+2212 Minus sign.

• Correct (minus sign)             +12 − 14 = −2

• Wrong (hyphen-minus)       +12 - 14 = -2

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