Sextants are navigating instruments used to calculate the distance between two points. They were used extensively on ships before the invention of GPS (Global Positioning System). Even today, big ships are all required to carry working sextants, and navigating officers have regular routines to keep themselves familiar with operating them. Despite all the GPS, gyro compasses and radio communications; at the end of the day it is an instrument that does not require any electricity or power of any sort to make it work. So when all else fails, the sextant is always there!