A Quadrant is an instrument once used by navigators, astronomers and surveyors. It is an instrument used to measure latitudes and altitudes. It gets its name from the mathematical quadrant, which is a quarter of a circle.
The mariner's quadrant had two sighting holes along one side. A lead weight hung from a cord attached to a brass ring at the corner of the right angle formed by the quadrant's straight edges. While the navigator sighted the Pole Star through the sighting holes, his mate read off the angle indicated by the weighted cord against the scale. This gave the angle of elevation of the Pole Star above the horizon and this angle was the same as the latitude of the ship.
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