I've got lousey hearing, but even I can hear when the RPM start to drop.

What I HAVE seen is people throwing a prop because they are trying to hit 11,000 RPM with a 4-stroke, OR the 16,000 RPM their manual says their 2-stroke has it's highest horsepower at.

Allfat, the way you are doing it is correct, but too many people use a tach to hit a "Target" number - which is NOT a good thing to do.