Hi George, I just look at the position of the cam signal relative to the crank signal at idle.When worn the leading edge of the cam signal is always just on or after the tooth just prior to the TDC referance gap.When ok the leading edge is between the last two teeth.Done dozens of these and never had to check any at a specific engine RPM always shows up at idle mate. Hth Sean Ps the signal does vary with differant engines ie micra is differant,so best capture a good sample of as many as you can.