TLDR: <0.02mm should be possible w/open source using cheap fabs. Interesting project. The hardware guy earlier built a rotary encoder and a vape pen. I am no m

TLDR: <0.02mm should be possible w/open source using cheap fabs. Interesting project. The hardware guy earlier built a rotary encoder and a vape pen. I am no metrologist (though by chance I once worked for the UK guy who brought Hexagon to China and made bank), this looks overall like quite a complex scheme that was probably referenced from an existing implementation. These days you can get 0.10mm pitch tracks and offsets ("4 mil") or 0.09mm ("3.5 mil") from JLC on 2 layer/4+ layer. With flex PCBs you can get still smaller pitch ("3 mil"). Combining a few rows of these with basic multi-track rotary encoder theory should give you portions thereof, ~0.01-0.02mm. This back of hand calculation aligns well with my Mitutoyo's test report, which states maximum permissible error is 0.04mm @ 5mm diameter, 0.02mm @ 0-200mm, and 0.03mm @ 300mm. Indicated errors on the test report are all in the range of 0mm-0.02mm except inside radius which is 0.03mm. This would be a standard high grade caliper level of precision. In practice, achieving these levels is going to require machining high grade steels and mounting them at high levels of parallelism, not simply working out the electronics. See also: https://www.eevblog.com/forum/projects/absolute-capacitive-rotary-encoder-(acre)-constructed-out-of-two-pcbs/ https://www.eevblog.com/forum/projects/absolute-capacitive-r... (see animation, GC7626C datasheet) https://github.com/littleboot/ACRE https://github.com/littleboot/ACRE