If it's a 2° cam key, it will move the cam 2° in the direction of the offset. When measured on the crank with the degree wheel, it will indicate a 4° change because the cam moves 360° to the crank's 720° (cam turns at 1/2 speed of crank). so move the crank 4°, cam will move 2°. If your timing set has three possible positions take a look at it. If you have a 4° retarded crank keyway you can just use that with the straight up cam key you'll be at 109.5.