Level-ologist?
Oooooh me, me me pick me!!
I'll be the levelolgist. in re: the Starrett brand, especially model #199Z.
Good levels are accurate. Accuracy range depends on intended use, but zero is zero. Here's how to check.
1) Somewhere, you have an area that is good smooth surface, and decent level; perfect isn't actually critical, kitchen countertop for example. Set it down, give it a couple seconds to settle, note the reading. Use 3 Post-its or 3 small strips of masking tape and put two on the counter along the levels edge, and one at the end. Pick level up, turn it around 180°, set it exactly same place (tape markers), allow it to settle. The reading must be the same, not important if level, but the same.
2) Get two pieces of wire, drill bits, straightened paper clip etc. Visually divide the level into thirds, set the wires in those locations, set the level back into position as close to tape markers possible, settle and turn it around. Again, the reading must be same.
What the wires accomplish, is removing 99.99% of what ever imperfections are present between level and the surface. A radical version could be a depressions or humps in level and surface that coincide.
You can see in any level, what a 1/16" or any dimension does to the bubble. A 1/16" will displace bubble a lot more on a 9" torpedo than a 4' framing level. If you level things accurately, this info is very handy.
Level a bench 12' long? Set the level down, parallel to length, of course it's way off. Use something small enough close to one end to zero bubble. I like using wood dowels, drill bits, depends on how far off.
If 1/8" gets zero, divide table length by level length and multiply the 1/8" that many times. If it happens to be a convenient amount, lets say a stack of washers, you'll be a little shocked how close the 'prediction' is.
When I level machinery, I've converted threads per inch of the jack screws into distance per revolution. Kind of a thrill to dial in with so little trouble, normally a tedious - hands and knees, up and down exercise you'll learn to avoid.
By the way, that Starrett 199Z? It's accurate to .0005 per foot; that's about 1/6th (one sixth) thickness of normal paper! It will react to drafts in the room, that cause contraction/ expansion. Leveling isn't magic or mysterious, but a lot of equipment enjoys being right.
