Here is something I had my fitters knock up for me

Basically it is a simple lathe - rotated by hand for the sole purpose
of checking the trueness of heli main and tail shafts. You can also use
it for straightening bent shafts and truing engine cranks.

The divider is just to illustrate how this is done - A dial indicator is
mounted in its place.

I had it calibrated with a test bar so it has an accuracy of one thou or .001"

  its really amazing...

It Awesome !!!