I just spent a bit of time playing with mach 3 , The value will keep dropping until it hits 2 , but if you save the value you want and then open the ports and pins dialouge box it seems to break the cycle of dropping by one and stays on the last value before ports and pins was opened. Not sure why but it seems to work

I think 5 is the max  you should set it to but not 100% sure as mine is always at zero so its not a setting I pay particular attention to. What to try however is setting it to the figure you wish then go to the config menu and choose the save settings option and see if that solves the problem.
Hood

mine needs to be at 11 or 12 for the spindle motor to spin up to the correct speed, at a value of 5 I cant get the output to my VFD over aprox 3 volts, needs 10 for full rpm (1725). I am not sure exactly what the value I am changing is but a few months ago when i was going thru the VFD setup someone here mentioned trying a much higher value.

Panaceabeachbum, Have you tried setting to Sherline mode in Ports and Pins, on port set up page? Would be interesting to see if it fixes the problem.

Brett

I will try that , config menu and choose the save settings option does not break the cycle , the only thing that seems to break the cycle is opening the ports and pins dialouge after motor tuning.

The earlier version of mach 2.5 or so did not have this issue , it started when I upgraded to a more recent version , its not really a problem once you figure out how to stop it , just a little glitch as the original poster pointed out