For what (little) its worth, you do know how to set up a level, yeah?
We were taught to plant it on a surface plate, the plate being only nearly level was fine. For imaginary purposes, picture a planar surface at 45 degrees inclination. If you put a level on that plane, it would be very obvious where the more or less correct orientation of the level would have to be, to get the bubble centered. This is the working principle of this method.
Rotate the level until you get the bubble centered. Place a straight edge, against the level (gently). We used parallels. Slide the level away from the straightedge without disturbing it, swap the level end for end.
Slide it back to the straightedge, and compare the readings. If they are not the same, interpret whether to raise or lower the adjustable end. Rinse, repeat. Which is to say, remove the straightedge, rotate the level about the bubble, until it is centered, replace the straightedge, and check again, both orientations. The level is in adjustment when it reads level in both orientations.
The levels we were using reacted quite a lot to the temperature of our hands in contact with them. No doubt as planned by the instructors. But be aware. Takes very little adjustment to make a huge effect.
Have seen a fair few Pool and Snooker tables set up. Beyond a long(ish) carpenter's level, the set-up guys generally just rolled a ball and watched how it rolled.
And a nicely set up table with new felt is a joy to play on!
I won't say ALL my youth was wasted, just the bits that didn't include women, beer, arcades, pool halls, motorcycles, etc... LOL!