lathe leveling has nothing to do with the earths level it has all to do with all axis's are perpendicular and parralel to each other and leveling is the medium in which to do.
years ago hardinge made a claim that thier cnc's could be run in any plane , upside down
side ways , whatever . becuase they were such a rigid machine.
upside down plays havoc on coolant leakage however
think of your tape measure sticking out 30 inches all twisted and turned from the starting point , imagine following that line with a tool what your work would look like |