Well redroush if you are dead zero'd @ 13 yds, there is a good chance that all of your shots will land high above POA @ 20yds,30 yds and probably be about dead on again by the time you reach 40yds. Lot's of variables of course (velocity, pellet weight,scope) so you really ought to take Stanley's advice on this one and check where your shots are actually landing at distances past 13 yds. You might find that you also need windage adjustments to hit your POA at the extended distances. Chairgun and other computer generated programs don't necessarily account for all the variables so don't neglect actual field testing.Have fun.