IMHO -- Stabila brand is the level to beat, 'tho they have some econo models as well. The #81S 9.5" torpedo I use is good to 0.5mm/meter in the upside position, which is really hairsplitting. OT, but the other tool I'd pay anything for and never give up, is the Armstrong Tools #64-005 torquing screwdriver for setting receptacle and breaker terminals to correct torque.
I'd check the platter for bearing wobble (run-out). If you can't borrow a dial indicator (I think it's called; ask a machinist or auto engine builder), I'd build my own. Use a RS soldering aid -- the weighted base thingie with multiple arms with aligator clips on the end. Clamp something hard with a smooth finish in one of the clamps, and place it so it just barely touches the platter surface. I'm thinking a toothpick for starters...Slowly rotate the platter by hand and see if the object touches the platter evenly around it's edge, middle, and inside. You might need some other jig to check the inside. You could also build a jig out of scrap in no time...
(What do the black lines on a bubble level indicate? Some kind of tolerance based on the level accuracy, I'd guess...)
I'd check the platter for bearing wobble (run-out). If you can't borrow a dial indicator (I think it's called; ask a machinist or auto engine builder), I'd build my own. Use a RS soldering aid -- the weighted base thingie with multiple arms with aligator clips on the end. Clamp something hard with a smooth finish in one of the clamps, and place it so it just barely touches the platter surface. I'm thinking a toothpick for starters...Slowly rotate the platter by hand and see if the object touches the platter evenly around it's edge, middle, and inside. You might need some other jig to check the inside. You could also build a jig out of scrap in no time...
(What do the black lines on a bubble level indicate? Some kind of tolerance based on the level accuracy, I'd guess...)