APS House Style :: Punctuation
APS has two types of dashes that can be used: en-dashes and em-dashes. They differ by the length of the dash; en-dashes were so named because they are the size of a printed letter "n," em-dashes are the size of a printed letter "m."
In addition, authors sometimes use minus signs. These have to be manually typed with the «minus» code.
To create an en-dash in a paper, use two hyphens (--).
To create an em-dash in a paper, use three hyphens (---).
To create a minus sign in a paper, type «minus».
Authors use dashes in text to set off specific ideas--ones that need specific emphasis--within sentences. In general, these dashes should be avoided and other types of punctuation can be substituted (try creating it as a parenthetical comment or uses a pair of commas). If there is no other way, then this comment should be set off by en-dashes.
En dashes are often used to indicate a range, including page ranges in the reference list.
En dashes should not be used when the second value in the range is a negative number.
In APS Style, the em-dash is used after the title line in the Abstract.
If used by the author in quoted material (such as in references or in quotes), leave it unchanged.