Here it is and I hope it helps. Its kind of involved but this is what I needed to do to improve the aim on a shot gun I owned and then I traded it off for a evil black gun and the rest is history. HJ and TT
Pitch - The angle of the butt of a gun in relation to the line of sight. In America, pitch is measured by resting the gun with its butt flat on a floor, the top of the receiver against a wall and its muzzle pointing up. The distance of the muzzle from the wall is the gun's pitch down. In England, pitch is determined by measuring the length of pull, separately, to each of the heel, the middle of butt and the toe.\
Cast Off - An offset of a gun stock to the right, so that the line of sight aligns comfortably with the right eye while the butt of the stock rests comfortably on the right shoulder. Almost all right-handed shooters benefit from a little castoff and most custom built guns are made this way. The only question is how much. The castoff of a gun is about right when, with the gun comfortably mounted, the front bead lines up with the center of the standing breech. A stock offset to the left, for shooting from the left shoulder is said to be Cast On.
Drop - The distance from an imaginary straight line of sight extended along the rib of a shotgun rearward towards the butt---to the top of the stock at the comb or the heel. (In British: Bend). All drop measurements in Hallowell & Co. listings are taken at the heel; that is, the distance between the imaginary straight line of sight and the stock at its very end. We will be happy to provide the drop measurement at the comb upon request.