A reader commenting on a recent post about the En Dash introduced me to a punctuation term that was unfamiliar to me: “the prime mark”:
Here’s one for you: teaching about the apostrophe versus the prime or foot mark. Same with the quote marks versus the inch marks.
I can only guess that this reader must teach students in specialized fields like mathematics, science, or linguistics, in which prime marks serve important purposes.
Like the apostrophe, the prime mark (or two or three) is placed at the upper right of a number or other symbol.
Unlike the apostrophe—which is vertical—the prime slants in the direction of the French accent aigu in the word élevé, but it doesn’t lean as far to the right.
Now that I know what a prime mark is and how it differs from an apostrophe, I plan to continue using apostrophes and quotation marks on the rare occasions I want to abbreviate feet, inches, hours, or minutes.
I can think of only two common uses of prime marks that one might see in a general publication:
1. To indicate feet and inches, as in this example from a feature in The Telegraph:
At 6’5” [sic] Gareth May is no stranger to the giant jibes.
2. To note latitude and longitude, as in these coordinates for the city of San Francisco, California:
Latitude: 37°46′29″ N
Longitude: 122°25′09″ W
A third use that I am familiar with is to indicate hours and minutes. For example, when timing a speech, I use the notation 1’15” to indicate “one hour, fifteen minutes.” In this context, seconds don’t concern me.
Then there’s the ditto mark. Apparently it differs from the double prime in some way because Unicode defines them differently, but most people use quotation marks when they want to use ditto marks to repeat items in a list:
1 ream paper red
” ” ” blue
” ” ” green
In specialized contexts, distinguishing between apostrophes, quotations marks, prime and double prime may be crucial. In general usage, however, apostrophes and quotation marks work just fine.
One concession a writer can is to use straight apostrophes and quotation marks instead of the curly ones.
For all you can possibly want to know about the significant uses of the prime mark, explore the Wikipedia article “Prime (symbol).”