This nut and saddle setup gauge is machined of aluminium with four troughs (2 each side) measuring depths of 1/32", 1/16", 3/32", and 1/8". Each slot can accommodate a 1/4" wide nut or saddle. You simply place the nut or saddle in the trough and draw parallel lines on both sides of the piece, depending on how much material you want to remove. It's quite simple: say you want to lower the action by a certain amount. Measure the height of the low E string over the 12th fret. If you want to lower the action by 1/32", you remove twice as much from the bottom of the saddle, 1/16". Place the saddle in the groove stamped 1/16", mark it with a sharp pencil on both sides and sand on the belt sander or use a file. Note that the thickness of the gauge itself, 1/4", also serves as another depth stop, giving you a total of five different depths.