For what it's worth...

For my NuTool MD500-30 (RF30 clone) I levelled the stand, then shimmed the base until the table was level.

I trammed the head, with a dial gauge mounted on a long bar (horizontally) mounted in the chuck so it could spin around several inches to the left, right, back and front of the table. I used a smooth parallel block between the rough-ish table surface and the dial to get a consistant zero.

I shimmed the base of the column with the thinest shim stock, until the it dialled zero (+/- 0.001-2) all around (the column flexes more than this if pushed :()

BTW I stripped the machine and rebuilt it, from the floor up. The columns are shimmed from new!