Altimeter, Sensitive, Type C-12, 50,000 ft, US Army Air Force WWII
Here is an early WWII-era Sensitive Altimeter, Air Corps US Army Type C-12, made by Conn, part number 80000. The C-12 Altimeter was used across all aircraft of the Air Corps US Army, including heavy bombers B-17 and B-24, medium bombers, B-25 and B-26, Fighters P-38, P-39, P-40, P-47, and P-51, and transports C-46 and C-47, according to the Maintenance Interchangeability Chart dated Dec 1943.
The knob is used to adjust the altimeter to the barometric pressure as displayed in the small window at the 3 o'clock position. See spec sheet in the photo gallery.
It is in very good condition given its age. The glass and case are intact, and the knob rotates, changes the barometric display, and the pointers move. Measures 3.25 inches diameter and ~4 inches deep.