Two degrees error in the calculation and you've got the wrong answer.
Which is bollocks of course as you can't fly that accurately anyway.
I got one of those "wrong" in the IMCR written exam - what I measured came out exactly half way between two of the multiple choice answers, and I picked one at random, and got the wrong one.
Real life question: if I'd flown that route according to my plan would I have hit anything or infringed controlled airspace? No, so that should have been counted as a correct answer.