Rigid Tapping--How is this accomplished?

Dear Fellow Group Members:
I would like to know how rigid tapping is implemented. I know
that the Z-axis feed and the rpm are synchronized such that the
Z-axis feed (in distance per minute) is equal to motor rpm x thread
pitch. How does the drive motor "measure" its angular displacement
or speed? Is the Z-axis speed adjusted continuously as a function
of motor speed variation? Or, is the motor angular momentum such
that there is no appreciable decrease in speed over the length of
the cutting of threads?
Finally, I imagine that there is more than one way to implement
rigid tapping. Any comments appreciated. Thanks, Jim