Now that level vial response is not what one would expect!
I salvaged mine from a unused tool. So I can’t recommend a source.
However, When reviewing specifications of a vial manufacturer/distributor, here is what one finds: Sensitivity ranges from of 31’ to 62’ per 2mm displacement.
If I understanding it right, this means a 2mm lateral displacement of the bubble in this case amounts from 31 to 62 minutes of a degree. That is 0.5 to 1 degree for 2mm.
According to the analysis presented above in the first post of the current topic, that is dividing the 3degree example error by 3 to 6. Thus causing a 0.25mm to 0.5mm center drop or lift on the top edge center.
Now is that a small error? At least now we can estimate it!
Anyway, all that is if you vial is behaving within that specification. And that is uncertain because normally, a vial would be balanced.