spindle speed reads (-)

[Spudys]

I am having a same sort of problem. I have tried changing the pulley ratios from 1.4 to .75. My motor does 1430 RPM and the lathe spindle does 2100 RPM. if I have anything else but 1 in the pulley set up screen. the spindle speed read out of the screen will not read the correct spindle speed. I am checking this with the rev counter so I know what rev's the spindle is doing. I have tried to correct this with the trim pot on my PWM to 0to10v board but it is always reading low even when I have wound the trim pot right up.
Why does the spindle read out change on the screen when you play around with the pulley ratios?

Cheers