Stringline the stairs of the Acropolis. Not straight. Center rise.
Mark One Human eyeball distorts. Crowning make them LOOK straight. Oterwise they would APPEAR to sag.
Imperfect world. Ever' body has to cheat to make it APPEAR 'more nearly perfect'.
Same with working on old houses. My brother was helping me put in some replacement windows a few years ago and going mad trying to get it level and get the windows to open and close right.
Problem is, the house itself ain't level to the ground anymore, and window frames not completely square. Got to just slap the things in and split the differences best you can to make it look good, while still functioning as intended.
Remember, perfect is the enemy of good.
As you have touched up on in later posts in this thread, we can get all scientific with it and try to get things within the millionths - but even when you get to a few tenths, sometimes you don't want to breathe on it for fear of effing it up.
Again, as has been mentioned, very few instances where you
need it to be perfect. Otherwise, good is good enough.
Therefore, I usually measure the fit by asking: Does it work for what I am doing and am I getting the desired results? If my runout tolerance is .001 and the collet runs .0005, I won't nitpick that - SEND IT! If my tools are all sharp and and properly supported, but still getting chatter, I figure a re-bore (on the soft collets) or replace is in order. Problem solved in a lot of cases.