Protractors may have diameters as small as two inches or in excess of twelve inches. In part because of these different uses, protractors have been manufactured in many shapes: the familiar semicircle as well as circles, rectangles, squares, quarter-circles (or quadrants), and sixth-circles. By the 18th century, the makers of mathematical instruments were explaining the manufacturing process for protractors, while the objects were beginning to appear in surveying textbooks and in introductions to geometry.īy the 19th century, machinists were devising a variety of specialized forms of protractors.ĭraftsman’s Protractor By Brown & Sharpe, 1887īy the 20th century, protractors had become commonplace in school mathematics. Regardless of who was first to describe the instrument, protractors entered the standard practices of navigators at sea and surveyors on land by the early 17th century. It is not clear that Blundeville invented the protractor, for other European mathematical practitioners wrote about similar objects around the same time period. As the title indicates, he used the protractor in the preparation of maps, particularly navigational charts for use at high latitudes. Although there were earlier instruments that were used for angle measurement in addition to other mathematical tasks, Thomas Blundeville described a tool specifically for drawing and measuring angles in his 1589 Briefe Description of Universal Mappes & Cardes. The protractors in the mathematics collections of the National Museum of American History (NMAH) illustrate stories of technical work and innovation in navigation, surveying, engineering, and war. However, protractors are not merely tools for enhancing learning but rather have a lengthy history of application in a variety of fields. Perhaps many people then never have reason to consider these objects again. Americans typically encounter them in elementary or middle school, when they are learning to produce reasonably accurate geometrical figures in order to explore mathematical relationships between those figures. Short reviews of the various science resources and curricula I have used with my own children.Protractors are mathematical drawing instruments used to draw and to measure angles.
Protractor angles how to#
Numbers: one set goes from 0 to 180, the other set from 180 to 0. Which one you read depends on how you place the protractor: place it Take care to read from the right set of numbers. A protractor has two sets of