[molf]

Adding to this: ALWAYS use spaces as thousand-separators.

Resist the temptation to use commas or dots as thousand-separators. Seeing a number with a dot as a decimal separator instead of a comma will be fine for most people (even if proper localisation would mean using a comma), but if you throw in commas that mean something else you WILL confuse people. And I imagine the inverse is also true.

[stronglikedan]

A space between numbers makes two separate numbers.

[stronglikedan]

I would love to hear why that's wrong, when we use whitespace to separate pretty much everything in textual representation.

[NikkiA]

Well, SI did standardize the thousands separator as space, so there is at least precedence for using spaced numbers there.

I personally don't like it though, and tend to prefer either the swiss system (ie, 3'800'000.0), or maritime system (ie 3_800_000.0) if separators must be used