Moonglum,
After the first 60 tries (yes you read that correctly) I was still unhappy with the final cart position which often ended up with an estimated 0.2mm offset from target in any given direction(!!!). I finally got the perfect result (and was only truly happy) after 70 tries...
Interesting to hear your take - I would imagine that +/-0.2mm is pretty good and that 0.5mm is more typical. I have played around trying to estimate how accurately I could set the offset angle, as I think that is the real unknown when it comes to talking about accuracy, and reckon +/-0.25 degree is the variation.
However, no protractor manufacturer, as far as I know, actually says either how accurately their protractor is made, or how accurate, precise and repeatable are the setups typically achieved with their device. In particular, regarding offset angle. So, is a Mint more accurate than a Denessen, a DB, a Wally tractor, a Feickert? How to measure this?