How did sailors measure longitudes and latitudes 100 years ago? 

The first sat nav device, called the sextant, enabled sailors to measure longitudes and latitudes 100 years ago. The sextant was designed to find longitude by measuring the angular distance between the moon and a nearby star. It was also used on land and to find latitude at sea. A sextant is similar to an octant, but more powerful and precise. The arc extends 60 degrees or more and measures angles of 120 degrees or more. Sextants were traditionally made of brass, with scales graduated on sliver. Modern sextants are often made of plastic. Most have telescopic sights. Therefore, sailors knew their exact position and thus would be able to adjust the course as necessary and check on progress.