Joules.
I have bored the chuck's locating recess, some .005 oversize. This allows a small amount of adjusting float, when mounting the chuck.....
I always use the same key hole, in the chuck. When needing a precision hold.
Consequently. I hold a length of 5/8" ground bar. (Old, reamer shank). In the accurate position. Then clock this true, tapping the chuck, with a lead tup. Tighten the chuck retaining nuts.......
This gives me repeatable accuracy, whenever using the same key hole.
So, as not to wear the single key insert. I use the other two positions, whenever possible.