How do you pronounce the symbol $'$ in $f'$? I'm not a native English speaker. A quick Google search revealed the symbol's name is apostrophe, just like in French. When used in a mathematical setting, I usually call it prime, so for instance $f'$ I'll read $f$ prime. That's the way you call it in French, but I just realized I didn't actually know whether that was the way you call it.
Thank you!
 A: It varies with the region.
"Prime" is how you pronounce it in American English. Here is a nice reference for American English pronounciations of math symbols; $f'$ is on the top of the second page.
"Dash" is how you pronounce it in British English: Here (search for dash).
A: $f'\rightarrow$ f prime
$f^{\prime\prime}\rightarrow$ f bis
$f^{\prime\prime\prime}\rightarrow$ f tris
$f^{\prime\ \backprime\prime}\rightarrow$ f tetrakis 
However most people do not know these words and just say double prime, triple prime etc.
A: In high school and junior-high school in Japan, we read a' as "a dash".
However,  in universities, it is occasionally read as "a prime" due to American influence.
I am not native speaker of English; therefore, I explored dictionaries and found a description. The Oxford English Dictionary vol. XIII (1970) states that it "usually read as `a dash' " in the explanation of the word "prime".
I feel something odd in this statement, but in the explanation of  the word "dash" in OED vol. III (1969), I found that "a stroke or line (usually short and straight) made with a pen or like, or resembling one, so made ....".  I am now realised the symbol ' should be recognized to be a short script.
I would like rather ask why American reads a" as double prime. Why the prime (= the most important) is not only one?
