The double sets of screws are for windage adjustment. You should alway zero the scope for right and left with your rings and your scope windage in the center. Count the clicks and get it centered. I count the turns on the ring scerws so I start out with the rings centered on the bases. Then to adjust your windage you can move the front one way a little and the back the other way a little.Broken crosshairs come from running nearly out of adjustment. Shim the scope up or down if needed as well to save all of your adjustment for fine tuning. I am not the best at explaining things but I hope you get the idea.