Strelok Pro is a fantastic tool for calculating adjustments for longer range shooting (past your point blank range). This fantastic app can be used on Android or iPhone and is a formidable asset for any shooter wanting to extend their distance, whether you're an air gunner or a long range 50 BMG target shooter.
The first step is to input data for as many of the columns as you can: BC, muzzle velocity, zero range etc...
Once you have done this, check your drop data a good distance past your zero range, if the adjustment Strelok gives you is correct, great, try it further out. If the data is off, adjust until your elevation is correct and enter the elevation you actually need in to the trajectory validation tool and recalculate your velocity. This does not mean your velocity from your chronograph is wrong!
With your new velocity, shoot at a much further range and see if your data has been calibrated correctly, it may need fine tuning or you may need to check your other data inputs and adjust them until you get the correct adjustments.
Because Strelok calculates a velocity for you to use that smoothes out your data, you don't even need a chronograph to be able to do this and it works from air rifles to centerfire rifles if you put in the best data you can!