National Museum of American History

As noted in the Introduction, the earliest use of protractors was probably in navigation. Protractors assisted with laying out angles to indicate the actual or desired direction of a ship. Makers might have also marked protractors with additional scales to be employed in computing a ship’s speed or direction, such as rhumbs or seconds. When coastal surveying projects were conducted in the 19th century, navigators used substantial protracting instruments called station pointers both to ascertain their position along a coastline and to record the topographical measurements of that coastline. In the 20th century, protractors were also utilized in aviation navigation.