FYI - It is my understanding that screw mapping works only when running G-code, not when jogging. Basically, it's not particulalrly useful in its current state....
Per Art:
"Screw mapping only works in Gcode. Since Mach3 is a pulse buffering program, its not possible to map for Jog modes and such, so the mapping was written only for program runs in the interpolator. Its rarley used, and I havent looked at the code for a couple years on it. So much work has been done on the interpreter over the past year or so I cant guarentee that its still functional, but you can only expect a result in Gocde run's. Last I looked it was still working fine."
Regards,
Ray L.