Featured Mystery tool identification

Any help with identifying this mystery tool would be much appreciated! The needle moves left and right while “opening and closing” the small part on the bottom right as pictured.
The inside has writing and numbers and is removable. It has writing on both sides. Measures roughly 5” tall and 2.5” wide. Thank you for taking the time to look!

 

Something to do with keys... those are key company names.

 

Tumbler gauge
Hand made
I'd think it would be worth hundreds to the old padlock crowd

 

Interesting... and some arcane knowledge there.

 

Nice piece...hand marked, an' possibly hand-made. Got some age, too...I agree with Terry.

 

Would that be for marking out keys for cutting? I Googled tumbler gauge and it showed images of a drinks glass with planes cockpit gauges on the sides

 

Definitely does seem like a tumbler gauge and that you everyone for your responses and help so far!

 

You should be able to (roughly) date it by the active dates for the key companys.

Debora

 

And by the fact that it seems to be a one-off. Possibly something a locksmith made for his own use. (not that I know jack about locks, but I've known my share of tool guys. They make things for themselves if they can't find something premade that will do the trick.)

 

@Bev aka thelmasstuff