Altimeter, Tycos Type C, 25,000FT, WWI Aviation Section Signal Corps US Army
Here is a Type C Altimeter used in early military aircraft of the US Army Air Service during WWI. It is labeled as having been manufactured for the Aviation Section Signal Corps US Army, which was active from 1914 to 1918. Crudely measured altitude from 0-25,000 ft, which was pretty high for aircraft of that era and requiring supplemental oxygen for the crew to exceed ~12,500 ft based upon modern standards. The purpose of the knob was to rotate the face of the dial while the pointer remains fixed to set the present field elevation.
Measures ~4.75 inches diameter and ~1.75 inches deep. It is in reasonable condition given its ~100 yr age. The knob does not function.