Gary I guess I errored a bit. Since my garage floor was not poured level I just use a level to insure its close and all four legs are on the same plane. Meaning it does not have gaps under the feet. I install bolts to insure it does not walk around when in use but do not tighten, just snug. When you tram a mill table or router table to the head with a dial indicator it insures it will cut true. A lathe test bar shows the bed is not twisted.
Here is some discussion on the subject from Practical Machinist but since CNC does not allow hot links from another board I have to do a edit
Well I can't get it to work, thanks CNC Zone but go to Practical Machinist and do a Search for this > Thread: How important is leveling a lathe or mill 90643 No Links allowed here! I found with a Google Search