Originally Posted by
mrrabbit
Roundness doesn't really quantify the quality of a rim - consistent rim extrusion does.
You can have a perfectly round rim on the outer circumference - but have very uneven tension between spokes because poor extrusion quality results in poor inner circumference consistency.
I don't think anybody discussed how to measure roundness. My measure would be a consistent ERD all the way around (within a mm). I think that would include your criterion of consistent rim extrusion.
Similarly, I also check a rim for wobble by placing against a plate glass window.