Why does this bubble level have spirit tubes in pairs?

Question

Please can someone explain the function of this level? Why the two torpedo tubes beside one another and why don't they match?

Answer 1

A careful carpenter will flip a single-vial level 180 degrees to check for deviation in a level or plumb line. This arrangement improves accuracy without the need to do that.

Also, some levels have vials which are curved as opposed to having a center bulge. In that case, you'd read the tube with the upward-arching tube. That's likely the case with this one, which is why the bubbles don't seem to agree.

Then, if you have both arches at all locations you don't have to flip the level over to have one at eye level.