Inaccurate Tach

[KyleTownsend]

Those are all good points.

I do know that this is the same instrument that a lot of shops use when they do annuals, etc. so I felt OK about it.

Also, the disparity between the published performance numbers and what I was actually achieving in cruise using the POH power settings led me to believe that either the MP or RPM gauges were innacurate.

Setting the RPM with the digital tach, my performance numbers are now within a few knots of the book numbers, which tends to confirm my suspicion.