I use many methods at once. For starters, I never pull a bow back until the tiller at brace is perfect. As long as its perfect at brace, the tiller wont be far off at all at draw. I also use shadows. I have my wife pull the bow while I look on. I will also lay the bow against the wall at brace, and measure the distance from the wall to each tip. The tip that is closest is the strongest limb. Other than that, Mirrors, cameras, or hang it from a tree by the handle and dangle a weight from the string. I have dont that, but that causes allot of set.