i'd love to draw it here but i can't... the divide by zero was a potential issue if there ever was a divide by zero but i think that would just crash.

the actual problem was inherent in atan:

imagine dividing 360 degress into four quadrants. in the first and third quadrant tan a (where 'a' is an angle) is positive, and in the second and fourth quadrants tan a is negative. the trouble is, there exists tan b where b is in the third quadrant that is equal to tan a where a is in the first quadrant (and same deal for second and fourth quadrants). so when you do atan x, there are always two possible angles it can be. the atan function resolves this by dealing only in two quadrants, so +-90 degrees. atan2 still deals with one number (x/y) but based on the signs of x and y it can figure out which quadrant the angle is in out of all four quadrants, giving you +-180 degree range.

so basically your code would work fine for perhaps half the angles, and then do the exact opposite for the others until you changed to atan2.

i hope that makes sense

julz