Apparently, it is the FIRST device EVER built by Peterson (the tuner manufacturer).
It features no needle nor graph (does NOT electronically/mechanically detect the tuning of other instruments), but is a TONE GENERATOR, and was used to tune organ pipes (matching - "by ear" - their tuning to the tones of this device).
I was also told that (with "Chicago" on it - as they very shortly moved to a suburb) it may well be from the company's first year of production.
Reportedly (??), no one working at Peterson has ever seen one of these - other than in pictures.
It WORKS - with a few quirks...probably due to a slightly weak tube or two...
It's QUITE loud, but - if not loud ENOUGH - (as shown below) there is an "output" female phone jack.
Anyway...I'm really amazed (honored/embarrassed) that I was given this device.
It's not something I'll use often, but will enjoy displaying and demonstrating it, and think of my good friend every time I happen to glance towards it.