This is an official US Naval aviation instrument, an altimeter, made in Rochester, NY, for use in the first world war. It is nearly 100 years old. Made of metal and glass, it is in very good condition, with very little wear. It is made to measure altitude up to 20,000 feet. The quarter markers of 5, 10, 15 and 0/20 are intentionally darkened for easy reference for pilots.An amazing piece of US military history.