Say that someone describes some amount as "100 plus or minus 5." Would you literally interpret this as "100 plus 5 or 100 minus 5," which is to say "105 or 95"? Or would you recognize that it's an idiom -- referring to the mathematical ± symbol, which is itself literally not the same as its components (plus and minus) -- which clearly means "95 to 105"?

If someone says "this estimate is off by a factor of 12," would you insist that it's ambiguous, because it could mean either "the estimate is 12 times [or 1/12th of] the right result," or "this estimate is off by 1, 2, 3, 4, 6, or 12"? Or would you recognize that, in actual English usage, there's no ambiguity at all (except perhaps in extremely unusual circumstances created by unusual contexts)?