The quadrant was the earliest astronomical instrument converted for nautical use. It was used to determine the altitude of the Polestar or sun and, concurrently, the location of the ship in degrees of latitude. Unfortunately, the difficulties of keeping the instrument exactly vertical and preventing the plumb bob from blowing offline on the windy, rolling deck of the ship made its use at sea difficult. The instrument was made of wood, or brass, showing a stereographic projection on the plane of the equator. This instrument was used to find the hour of the day, the sun's azimuth, and also to take the altitude of an object in degrees.