Ruler distance is wrong for anything but exclusivly horizontal or exclusivly vertical lines

The ruler counts every field stepped on as 1 unit of distance (equal to however large the squares are set to). Here is the problem with this: The diagonal of a square is not equal to the length of its side. The length of the diagonal of a rectangle is equal to the square root of a²+b². If you moved 10 meters north and 10 meters west, thats the square root of 200 which would be  the distance you be 14.142 meters(rounded to third decimal). If you moved 10 meters north and 2 meters west, the distance would be the square root of 104 = 10.198(rounded to third decimal) meters and so on.

its more like it counts tiles, 10 tiles=10meters no matter if vertical, horizontal or diagonal. you can switch measurement to euclidean in the map options to get a closer (rounded) result 

Since this has been asked and answered, I'm going to close the thread. If you want to re-open the issue, RedNero, feel free to post in the dedicated  thread,  A Measured Update - Ruler Bug Report Thread . You'll get better visibility from the devs there.