The HTM Precision Bow Vise is used for setting up bows, specifically for shooting uphill or downhill. The up and downhill is the 3rd axis setting on your site. The HTM Bow Vise has a built-in leveling device. Once attached to a permanent structure, the upper housing has a patented leveling system. This patented system allows for accuracy in the leveling of the upper housing and rotating bar. The rotating bar is parallel to the top of the upper housing to within .001. Once the upper housing and rotating bar are level in 2nd axis, the bow is attached to the rotating bar with a 5/16?-24 threaded handle. By rotating the gear-driven handle 45 degrees downward, your sight level should not move. Then do the opposite. If the level is off, the vise will assist you in making the appropriate corrections.