After starting to use the siunitx package for typesetting units (and the numerals before the units) in LaTeX, I noticed that it typesets a single space between a numeral and a unit (a space that is not as wide as a normal space). I have tried unsuccessfully to find a proper reference that calls for this. Wikipedia mentions it on Space (punctuation), but the external reference given on the Wikipedia page, which is in this online .pdf brochure, does not say anything about thin spaces. It only mentions that there should be a space between numerals and units, but says nothing about the size of that space (in which case I think it is reasonable to assume that a normal space is referred to). I have added a question about this in the talk section for the Space article.
What is the proper size of spaces between numerals and units? It would be interesting to know the source for the usage of thin spaces in siunitx, and if that is the way it "really should be".
Best Answer
As I understand the official SI manual (which
siunitixis supposed to follow), there should be a space, not a thin space, between the number and the unit:I also find that this seems to be the more common procedure in typed texts (but that might again be because most people don't know abut the thin space).
Just to be clear, the SI manual is aware of the thin space, cf. the following section 5.3.4:
And precisely for this reason, the
siunitixpackage has since this question was asked changed its setting from using a thin space to using a normal space, see this update.