as stated earlier, a table doesnt need to be level, just square with the spindle. as far as accuracy of a level, in artillery we sometimes use a gunners quadrant, which must be very accurate when shooting several miles. that is done with what is called an end for end test. this test was mentioned in an earlier reply. there is a machined surface on the breech of the gun, it is leveled using the gunners quad. then, with out making any adjustments to the quad or tube, the quad is reversed and the reading is compared to the first reading. the difference is divided by two and that is the amount the quad is off. then that can be included in the settings for firing. as said earlier by another earlier reply, this can and should be done before trusting any level. there is such as thing as manufacturing tolerances, and with so much stanley type junk from china,,,,,,,,, oops, getting to political, sorry mark