Old mouse instead of encoder

I don't know in what topic to ask this, but what variable should be changed to make such thing?

I always wanted to try with a stepper system w/ encoders - hooking the Following error up to the motions adaptive feed in such a way that as the following error increased - the adaptive feed would decrease. (to a minimum velocity that the stepper could start back up)

I don't know how practical this is.

sam

such a way that as the following error increased - the adaptive feed would decrease

I want to try to tune PID for position. But I'm new in linuxCNC completely. I need to read documents for it at first.
What manual is better to read for this.

I wonder what variable is related to task and what to feedback to make nets with them.