I would site the scope in at 25 yards at the 3 power setting, then move to 50 and make any necessary adjustments and then move to 100 and after you have it set, recheck it on the highest power setting. Then you should be good to go. A lot of the older cheaper scopes tend to drift the point of impact when you change power settings. So it is best to just put it on the 3 or 4 power setting and leave it there.