Nogyro - you hit it on the head - as long as the numbers do for you what you want them to - its all good. Its when people start comparing numbers and saying their engine does things the factory has not even seen is when things get fishy. These cheapo tachs are really only accurate to within 5% ... at 10000 RPM that can mean as much as +/- 500 RPM.. I have seen them be 10% off.

On the other hand - as long users only use them as a tool for general tuning their specific setups and not get too hung up on comparing them with everyone else... it makes sense. I gave up using them a long time ago because I can hear and feel the difference immediately betweeen props and needle settings.... yes, that took some time and experience but its not difficult.

A far more valuable tool than the tach is a thermocouple temperature probe... tune the engine by temp, and not RPM will provide a much better result and most likely lead to a longer engine life.

There is no doubt that different props act differently, even on different cowl designs.. no matter what the tach says on the ground though you really never know until you fly!


DP