Oh wow! I think I could even guess how it works! The gas (or possibly liquid) from whatever the gauge would be attached to, would travel up and around the axis of the needle, pushing the lever down, which would turn the level's fulcrum (axis) at the other end, that would move some sort of gearing and the gearing would work against a spring that holds the needle! ^.^

It also looks like it could easily be repaired (if need be), as long as replacement parts were available. ^.^

Love the fact the Bourdon tube is exposed so inspections can be easilly made for soundness. I assume this would aleviate a number of questions on inspections.

Almost all modern mechanical pressure/temp gauges work in this manner even today. Just behind the cloak of the dials face. Reminds me of an air brake pressure gauge.

I can tell by the logo that this one was made by Crosby for registering steam pressure. Never seen a steam gauge with the numbers and increment lines painted (or etched?) on the glass like that. Very unique. I have a gauge collectors guide book, I'll have to see if I can find any data on it.

Cool!

I enhanced it myself to see if I could read the brand, but didn't need to when I checked on what the trade dress branding looked like. It's certainly a Crosby gauge.

As for the face, I'm going to guess that it was a promotional/display item produced by Crosby.