Put up a target at 100 yds preferably with numbers across the top like a MOA sight in target. You probably already have it zero'd for 100yds. Remember your zero elevation if you dont have zero stop. Look at the numbers at the top of the target. Now turn your elevation knob all the way up and look at the numbers again. Turn the elevation knob all the way down and look at the numbers again. Ideally the numbers should look the same. Crisp and clear. In all probability they will look a little blurry at the top elevation and less so at the bottom of elevation. Not good if you need to dial up a scope to near max elevation to shoot at 1000yds or more.