Yes, it is a quadrature encoder. 4 * 5 * 1000 = 20,000.
Not sure if I really have 1/20,000 (0.00005) resolution though. I'm not 100% sure how that works. I guess I need to start watchig Fleabay for a good deal on an oscilliscope. And see if I can really associate all 4 pulses with actual movement. How do you measure 0.00005 anyway?
I would have been happy 1/5,000 (.0002) resolution. Its better than the claimed original repeatability of the machine. I guess I will have to buy some quality measuring stuff, find my backlash, make some cuts, and do some measurements to really know.