[rthibeau]

Not a sailor, but I believe the lathe is levelled to the floor, bench or whatever it is mounted to. The work is held level relative to itself, so it could be used upside down or at any angle...in theory. The leveling to the mount is to keep the ways from twisting thereby throwing the accuracy of the lathe off. The rocking of a ship is on a different level and doesn't apply to this leveling.