I am quite sure that is not the original rear sight. I would place the elevator on the lowest notch(closest to the barrel) and try it at close range to see where you're at. Usually with open sights if you are on the bull at 25 yards you will be close at 100 yards. A bullet crosses your line of sight twice, once one the way up and once on the way down. If your shots hit to the left or right of the bull, move the rear sight in the opposite direction that you want your bullets to move on the target. E.g., if your gun shoots too far to the left, move the rear sight slightly to the right. This can be done by tapping the rear sight base using a copper or brass drift pin with a small hammer. Open sights of this variety are at their best at 100 yards or less.