Accuracy of the electronic tachometer on the R65LS

[ShutterPilot]

Slightly off topic - shouldn't the torque and HP curves cross each other at 5252 rpm? What's going on with this reading - is it scaled somehow?

[Barry]

Slightly off topic - shouldn't the torque and HP curves cross each other at 5252 rpm? What's going on with this reading - is it scaled somehow?  

It's just the different scales used for torque and HP.  With the same scale they would cross at 5252 because horsepower = torque x  RPM / 5252

Provided that is the units are HP and ftlbs.   I know my cross over point is 27.3 HP and 27.3 ftlbs.  

The precise number of 5252 RPM and how it's derived can be demonstrated mathematically but we don't want to go there as it involves calculating with radians.

[DanMay]

Back to the original tachometer issue.  I tried the calibration method using the adjustment screw and discovered that the RPMs get progressively worse at higher revs.  At 1000 RPM, it reads proper, but gets worse and worse as the revs increase.

I decided to calibrate it to 5000 RPM, and made a mental note of the skew.

[georgesgiralt]

IMHO the magnets in the galvanometer moving the needle are fading out. As the magnetic field is weaker, the force created by the current is not more proportional to the rotation of the coil. Thus the non linearity you describe.
Only one way to correct : find a better tacho.