From: Ed Popko
Date: 2016 Dec 11, 09:31 -0800
This is a sextant. It measures angles to things in the sky. Before radio and GPS, navigators on ships and airplanes used them to find out where they were. If you know the angle to the sun, star, planet or moon plus the exact time and the body’s location in the sky you can calculate your location anywhere on earth. It's even possible to tell the time of day or night by measuring the distance between the moon and one of those bodies.