On Wed, 10 Sep 2008 03:38:55 -0700 (PDT), Jim Wilkins
wrote:

You could watch both encoders on an oscilloscope. You might not catch
a single slip but you would clearly see multiple continuous ones.
I already have digital readouts connected to each encoder. So I know
how many counts each one is producing. The counts match exactly after
everything stops. The numbers change way too fast to see how close
they are during rotation.
Eric