Johann and I met up at Metrix: Create Space tonight for some brainstorming, and to work on projects. I'm working on kitting and packaging in preparation for a engineering validation and verification (V&V) build, while Johann is verifying his auto levelling code.
One complaint about the original auto-levelling probe is a systematic error that occurs when the probed position is different from what is in the probe level offset. Since I had my thermal printer on me for printing kitting labels, we came up with a really awesome way to verify probe offset:
(We heated up the hot end and had it touch off on the bed. Since label printers uses thermal labels that change color upon exposure to heat, each hit registered with a very crisp black dot on white paper. We then ran the G29 routine to observe where the probe actually hits vs the coordinate system of the printer.
In the final shot, you can see there is still systematic tilt in the bed, and the line traces for an over-compressed layer appeared darker / wider. The debugging and tuning continues).