Should a comma be used in a scientific quantity such as wavelength?
In astronomy we often use a unit called Angstrom which is a unit of length. The symbol is \AA. Should I write 3000 A or 3,000 A? How strict is the rule for using commas?
Solution 1:
This is a matter of style. There is no such thing as "the rule for using commas". There is no such thing as a rule, for that matter. There can be style guides that suggest this or that, or nothing. And you can write a style guide of your own that suggests whatever you want.
This means two things:
- Your field or subfield may have a preference one way or the other. Consult your peers, faculty members, or just your supervisor. Failing that, look at other papers in your particular field before deciding anything definitively.
- If there is no clear pattern to make out, you can use whatever you want — for as long as you are consistent. Pick one style and stick to it throughout.
Note that most style guides that do suggest using a separator typically do so starting with five digits, never four. Note further that many style guides suggest using a thin space rather than a comma.
Again: there is no rule.
Solution 2:
Because of the largest numbers associated with certain fields such as astronomy and chemistry (or very small numbers), scientific notation is preferred. The number of significant digits should be retained consistently. Astronomy and geology often use two significant digits; thus, your number could (should?) read 3.0 x 10^3 A