Terry Lee was kind enough to send this unique measuring technique. First level the trailer by checking several areas: In front at tongue, the middle close to the axle, and the rear with the level bubble. Then check the level of the boat: Using rod box lids, floorboard and bottom of pad about 6" from rear of pad with the level bubble. 

Laser pointer, level bubble from a small carpenter's square, clear plastic ruler and Scotch Tape.

Remove the prop and level the propshaft, using the powertrim, with the level bubble.

Hold the laser pointer on the nose of the lower unit with the level bubble on top.

Tape the ruler so the 2" mark is at the Pad. The laser will show you at what height the prop shaft is in relation to the Pad.