he link so you can see the app

http://www.android.com/market/#app=d...litach.android



Heli-Headspeed
Developer: bormisoft

Heli-Headspeed is a tachometer that measures the RPM of your RC model helicopter blades. For this purpose the blade sound is recorded and its frequency spectrum analyzed. Works with electric and nitro model helicopters with two blades. The process is simple: a ) select the expected RPM range and b) click the measure button.