In geometry, a protractor is a circular or semicircular tool for measuring and angle or a cirlce. The units of measurment utalized are usually degrees. Some protractors are simple half-discs; these have existed since ancient times. More advanced protractors, such as the Bevel Protractor have one or two swinging arms, which can be used to help measure the angle.
Athough protractors were used in school to help children learn angles they were also used to aid in navigation. A more complex form of protractor, or station pointerdesigned for plotting the position of a ship on navigational charts, was invented in 1801 by Joseph Huddart, a U.S. naval captain. This advanced the exploration of new places and the ability to chart and return to the same routes. A related instrument used by marine navigators is the course protractor. It provides an effective tool with which to measure the angular distance between magnetic north and the course plotted on a navigational chart.“ protractor." Encyclopædia Britannica Online. 25 Jun. 2009
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