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.