Roughly confirming the 3 micron accuracy

So, at 30,500 steps per mm in the GRBL driver I'm getting repeatable movement in 50 micron steps from the control panel. Given I'm 1/256th stepping the motors and I reckon they're only really good for 1/4 stepping, that roughly works out at 3-4 micron accuracy. This coincides with the original estimate of 3 micron precision from the first stepper motor tests under manual control.

If I try to move faster than that things slip, which is probably me overdoing the GRBL acceleration and/or max travel speed, so I'll tweak those down a bit and move on to the better microscope. Once that's set up we'll try scraping some squares out on a smear of Sharpie marker on the slide and see how square-ish things are. Probably going to need a bit of improvement to the control panel motion settings too.