The BFTA site have a good document on setting up scopes for FT here
. However I might have got a bit confused.
However a quick summary of the two main versions
This is where at each distance the elevation turret is marked so that for 40yds is one setting and then a 20yd one is another. Usually find that the turrets are custom made so they stop turning just past the point of where the ranges start going down. As in my case 20yds is the furthest 'down the turret turns to.
Using the scope at one magnification and zeroed at a distance say 35yds. You shoot at an mark on a target at every 5yds from 10 to 55yds. You can then use the actual pellet strikes in reference to the mildots on a scope for example. You then have a 'chart' with all the aim points for each distance.
With regards the scopes shooting I range at 45 shoot at 25 apart from standers at 15 mag.