The one I had had two set screws on it like a laser site. Since everyone draws and holds slightly differently, the idea is to attempt to draw and hold in your normal, "perfect" technique, then adjust the "bubble" to as close to center as possible. With continued shooting, you can then fine tune the retina lock feature. The idea is to set the retina lock so that you draw and hold the bow the exact same each time, once that occurs, then you set your site pins.