In paper tuning, one shoots through a piece of paper at a short distance like 6-10 feet, and observes how the arrow nock and vanes tear through the paper. The rest and serving nock are then adjusted to minimize the tear, in order to get the arrow pointing in the same direction it is being shot. The goal is to get perfect or a small 1/4" tear with the nock high and left. This especially helps when shooting broadheads as the broadhead will tend to plane (like a forward rudder) in different directions if the arrow is not initially pointing in the direction it is moving.
