Thanks for the prompt reply. The reason I was trying to use the tachometer on my heli is because the 9ZHP Instruction and Operation Manual states on page 27 that
"The tachometer function in the PCM 1024 transmitter may be conveniently used to measure the rotational speed of any propeller or rotor blade, up to a maximum of 50,000 RPM."
Since the tachometer is a useless feature for heli rotor blades and was designed only for airplanes, the suggestion that it can be used for rotor blades should be removed from the Instruction manual. Nevertheless, I think the 9ZHP is a very versatile TX.