What is this tool thread?

I have this gauge, what's it for? It stands about two inches tall. It says Lufkin, and Made in USA, but no other markings on it. It must measure the depth of a hole or something similar I think, because the zero mark is in the fully extended position. Any help to be had?

Here are the markings on the side of the tool.



This is what it looks like in the zero position.



And here's what it looks from the bottom, fully retracted.