[randallu]

It's interesting that none of the hobbyist printers I've seen have optical calibration like a servo does -- I've read about overshoot being a problem when doing faster prints, but if the head could measure where it was in XY then it shouldn't be such a problem. Some old Sun optical mice knew where they were on the trackpad (which was super annoying, you couldn't pick up the mouse and move it somewhere else for a long drag), so the technology shouldn't be expensive...