I just put a little chalk on the marks, then wipe the excess off.. works great. There is a bolt holding a flat clamp where the dizzy shaft goes into the top of the block, you loosen it. You will need a dizzy wrench, or at least I did, you have to set the timing with the engine at operating temp, and the offset wrench makes it a little eaiser on the hands.. then start the car, aim the light down at the timing pointer on the balencer, and turn the dizzy to change timing. If you have a multi spark ignition, its a good idea to put it in diagnostic mode first.. after setting it, tighten down bolt good, double check you didn't change it, then, put spout back in and reset ignition box as needed, button it up and see how it sounds/feels.