The problem I am having and can not seem to solve is the the Spindle True readout is not stable. I am using CNC4PC's C3 Index Pulse card. When I was using Mach3 VerR3.042.032 everything worked fine. I could set the rpm with my VFD (using pot) say at 400 rpm, verify with rpm reader, and S True would read 400 rpm and vary only 1 or 2 rpm. Since I downloaded later versions (currently have VerR3.042.037) the readout is not stable. For example, at 400 rpm, it will hold 400 for a few seconds, then fluctuate down (varies each time to different values 360, 375, etc) and then back to 400 rpm. I've searched thru CNCZone and Mach Forum for threads and also read the document "Threading On The Lathe - Mach3 Turn".
Any suggestions? Need to cut some threads, however with the readout not stable, don't want to attemp until solve problem.