cloudhopper,

Its a little difficult to explain without a picture (hopefully minnflyer will provide one of his) But you can buy a deflection gauge or use a ruler. Set the surface to be centered by eye first then Stand a ruler up next to it the deflection is measured from the outside edge of the surface. How far up, down or left, right it moves from the centered position is the deflection. Agian in this caase a picture is worth 1000 words hope it helps more then confuses