Normally it's done by shooting a group of arrows at 20 yards, then shooting a group at 40 yards using your 20 yard pin. Then you do the same thing. Measure your distance between groups and campare it to a chart. Edersbow has one with instructions. Sometimes it's close, for others it's off by as much as 30 fps. It's about 15 fps off with my bow compared to what the local chrono says. I will check mine with your method and see how close it is, from glancing at it quickly I think it's way off. My bow drops about 6 or 7 inches at 30 yards from 20 yards and it only shoots 260 fps.

And you really don't need to shoot a group at 30 yards with your 30 yard pin, it should be in the center of the spot, right? Just shoot a group with your 20 yard pin and measure how far off they were from the spot you aimed at.

Heres a tip by the way, when you go to shoot the group with your 20 yard pin at 30 yards, your arrows should hit where the 30 yard pin is, since you are at 30 yards. So if the 30 yard pin isn't on the target, don't release the arrow.

Of course if your pins are a little off, this is going to screw the whole thing up. It will also make a difference how you sight with your peep. If you center the pin in the peep at each yardage, your bow will seem to have a flatter trajectory, because your pins will be closer together. If you center the peep on the sight housing, or use a No Peep your pins will be father apart.

Paul