What is this tool?

[Baz]

Originally Posted by herr_oberst

It's used for quickly measuring stacks (or "lifts") of paper for various print shop and bindery procedures.

Nice work, Herr Oberst!

[Eric Coffey]

Originally Posted by herr_oberst

you've got the wrong end of the "L" in the slot.

If your tool looks like an "L", you should see your doctor, ASAP.