I have used auto tune on some large VSD,s and motors, the function allows the VSD to learn the characteristics of the motor, it is done on initial initial installation and does not have to be done again, I hade some very strange results when I did not run it first, mainly the motor ran but did not develop any grunt. I think this parameter goes under several different names. Not all VSD,s have this function ABB drives did as far as I con remember, been out of it for a while. Again it could be a function to use in a PID control situation, if so nothing to worry about when driving a milling machine.