I use small slips of paper under the individual feet. Right now I used "PostIt Notes" 'cuz that is what i have on hand. I just add and subtract layers until the platter is perfectly level. Lucky for me both my TTs have three feet. But it would only be a little harder with four.
Turntable leveling...
I have a Rega P9/Lyra Delos and my cabinet is not perfectly level. My bubble level shows about 25% of the buble outside of the circle and digital reading shows about a -1.4° as the most declination on the TT. How important is it that I get it spot on? I would need to complete unload the cabinet to level it at it feet. It is a heavy cabinet with a marble top. The wt of the equipment in it probably exceeds 250 lbs.