It'll all depend on a lot of factors. What rifle it's on, how it's mounted, the power level of the rifle, the caliber, the pellets... a ton of stuff. Chairgun is good if you have all the info required and know how to use it. But best way is to set up targets at measured distances and just practice shooting it. You'll soon see the point of impact differences at different ranges, I.e. zero-15yrds, zero-10yrds, zero+10yrds, zero+20yrds etc.... This is the best way to work out your aim points for your individual set up.
Jim