I dont know if anyone still reads this thread, but I reply anyway.
Hey EDWARDO, I just tried the telemetry, or I am just hooking it up, i noticed when i put the RPM sensor on the front axle, with a black line painted on it, it would not only count the black line, but would also count the scratches on the axle.
So if you are still having trouble getting the rpm to read correctly, try maybe putting where there is no scratches on the surface, it worked for me.
You also could put a piece of black tape around the axle so the surface was consistent, and then stick the silver sticker on it or a white pen mark, or visa versa.
You can use the speed of this axle RPM to compare with other times you run, eg: 5000rpm on this shaft in run 1 of the day, is a bit faster than 4000 rpm on this shaft in run 2 of the day, Do you get what I'm saying?