Old school alignment guys; gauge mount idea. What am I missing?

92b said

Putting the gauge directly on the hub (clean and undamaged) most likely will result in not needing to do a rim compensation for camber or caster. Depending on how you measure toe and how accurate you want to be you will still likely need to do a rim compensation to set toe.
Don't forget before any alignment you first need to do an alignment qualification.

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Rim compensation? Not even sure what that is or how and if the laser alignment machines do that. How would I do something like that?

Alignment qualification?

I was guessing that any alignment difference between the hub, wheel, etc. was just ignored. The deal they clamped to my wheel last time could have been off a fair amount just due to the concave face of my wheel and the tech not even caring if it was up, down, left or right of the center of the wheel. I figured it was all more just a “close enough” type measurement.

Thanks!