Take your scale, and transpose it left to right so that you are using the opposite side (numbers will be backwards). By this I mean make sure that if you were using the left side grid of numbers, that now you are using the right side numbers (that will likely be mirror image since you will be looking through the plastic to etching on the opposite side).

This should eliminate any chance for machining errors. If it still reads 1 degree, then you probably have 1 degree of tow. If it reads zero, then you probably have a improperly manufactured scale.