Editing Apostrophe (section)

==Informal use in measurement and mathematics <span class="anchor" id="Informal use in records of measurement"></span>==
{{More|Prime (symbol)}}
Formally, the symbol used to represent a [[Foot (unit)|foot]] of length, depth, or height, is {{char|′}} (prime) and that for the [[inch]] is {{char|″}} (double prime).<ref name=CMOS>{{cite book |title=Chicago Manual of Style |edition=17th |date=2017 |publisher=University of Chicago Press |at=§10.66}}</ref> (Thus, for example, the notation {{char|5′ 7″}} signifies 5 feet and 7 inches). Similarly, the prime symbol is the formal representation of a [[minute of arc]] (1/60 of a [[Degree (angle)|degree]] in [[geometry]] and [[geomatics]]), and double prime represents a [[second of arc]] (for example, 17°54′32″ represents 17 degrees 54 minutes and 32 seconds). Similarly in mathematics, the prime is generally used to generate more variable names for similar things without resorting to subscripts, with {{var|{{prime|x}}}} generally meaning something related to (or derived from) {{var|x}}.

Because of the very close similarity of the typewriter apostrophe and typewriter double quote to prime and double prime, substitution in informal contexts is ubiquitous but they are deprecated in contexts where proper typography is important. There is also a risk of an automatic process "correcting" a typewriter apostrophe to a punctuation apostrophe, which results in another variant when a prime symbol was intended.