To add a little nitpicking to your nitpicking, it should've been a right single quotation mark (’, U+2017). In fact it's not an accent (´, U+00B4), but a prime

To add a little nitpicking to your nitpicking, it should've been a right single quotation mark (’, U+2017). In fact it's not an accent (´, U+00B4), but a prime (′, U+2032). Since none of these characters can be easily produced on a standard US keyboard, I suspect that the blame belongs not on the author but on his publishing system that thought he meant "4 feet" (or perhaps "4 arcminutes").