Tachometer flip of the dial

[Fly_Chick]

I have been posed this question, and have been unable to find an answer, so thought I would toss it out on Flightinfo.

How many revolutions of the prop does it take for the tachometer time to move forward 1/10th?

 

[CA1900]

Depends on how the prop tach is calibrated. Only at a specific RPM will 1 hour equal 1 tach hour. Some planes cruise at 2400 RPM, while others at 900 RPM, for example. No single number can answer your question.