I think you would have to cut two slots for it to get a reading. Have you thought about the deal that checks rotor speed on a heli? I dont know what it's called. It has a rotating disk inside of it with two slots. You look through it at the rotor blades. There is a wheel on it you turn that speeds up and slows down the disk inside. You simply adjust the speed of the disk until it apears the rotor head has stopped. There is a digital readout on it that tells you the speed the wheel is turning. If they wheel and the rotor turn at the same speed it looks like it's stopped. Pretty neat deal. My buddy says his cost about $90. Kind of high but a cool toy. Later David