used tobe, when a consciencious carpenter finished a frame, he walked through with a straight edge or by eye and checked all the studs for varience. by cutting a 45 degree curf cut approximately half way through the stud at the center of the bow and driving a wedge into the cut you can draw it to you and nail the shim in place. vice versa on the crowned side, you cut a little wedge out at the same angle and drive a nail in to the face of the stud-through the cut, drawing the crown away from you. if you over cut too much or the stud feels too weak sister a scab ( about three feet long ) on the cut and nail in place w/4 nails on each side of the cut. hope this helps and good luck. by the way, all the other postings are things i`ve seen work well.