Hi,
I don't know if the lathe set handles it differently but the index signal is taken by Mach, averaged and converted into
an rpm number using the range info on the spindle settings page and displayed in the True RPM DRO in the wx4.set.
This is done automatically by Mach, you have little control over it nor even view how its done.
Have you set up the range info? Configure/Mach/Spindle....in particular set up a realistic max and min.
Craig