X axis calibration sd3

I thought the wiki would have info but it really doesn't. In fact I swear the wiki just covers the y axis twice.. the one screw on the left of the X carriage only tightens one side of the belt, and that tension doesn't spread across the whole belt it stays between the X carriage and the X stepper. Am I crazy? Anyone have an obvious tip I'm missing?

I'm only asking because I'm getting out of round holes and circles.