For a while I’ve been looking for the correct character for separating groups of three digits when writing large numbers.
The MLA Handbook for Writers of Research Papers 5th ed. says,
Commas are usually placed between the third and fourth digits from the right, the sixth and seventh, and so on (70). I cannot follow this advice because “20,005” is ambiguous for an international audience.
Instead we turn to ISO 31-0 which tells us to separate groups of three digits with a small space. It seems natural to use the thin space character, U+2009. Unfortunately U+2009 is a space character, and lines could be broken at the character. The ideal solution seems to be to use the narrow no-break space character, U+202F. It’s unclear how many fonts support this character. Freefont does not seem to support it.
William S. Statler discusses this issue, and Jukka Korpela, as usual, takes a practical approach to this problem. I think for now I will stick to the non-breaking space, U+00A0, and prepare for a switch to U+202F when the time is right.
I don’t know what to do about the decimal marker. ISO 31-0 suggests using a comma, so I’m tempted to start using that. But no matter what I choose it seems like someone will get confused. Perhaps I can do something to ensure that I never follow the decimal marker with exactly three digits.