hi im trying to set my sons xmas present up for him and have zero ed it at 36 yards i have then been told that rather than use hold over which has always been my way being more of a hunter than into targets to use dial up! so i have tried to use chairgun putting pellet speed and the centre mesurements , pellet weight etc and i have printed the scope labels off but when i change the dials to the different distances they just dont seem to work out! like i said its spot on at 36 yards but then when i shoot a 50 yard target and put the dial on 50 yards its about 3" low...... im puzzeled