G'day Gray,

You know what, i just came in from the shed after doing just that!

it's gotta make more sense to get confidence in the contrast eh?.... i told you it was a dumb question.

i feel foolish, as i do know of others who do it this way...

the thing is that i was able to successfully tach other rotors using this method.

there is something about the data that doesnt make sense though, as i have three engines of sizes small, medium and large, and two rotor types, and unless it is a function of the rotor load curve versus engine power curve, then the numbers dont make sense.

i'll give it another go tomorrow.

Happy New Year!

Tim.