The birth of geometry (literally “land measurement”) can be traced to ancient Babylon and Egypt around 3000 B.C., as well as other cultures around the globe.
But what we think of as geometry today, Euclidian geometry, began around 300 B.C. when Greek mathematician Euclid began accumulating theorems and formulating his own. Euclid and his colleagues worked without the benefit of protractors.
Simple forms of the device, which uses a semicircular disk to measure from 0° to 180°, were invented as early as the 13th century. But the official first citation of the tool being used as a “Mariner’s Flie”—helping read a ship’s course—came in Thomas Blundeville’s 1589 book, Briefe Description of Universal Mappes & Cardes. Blundeville’s work also catalogues how the protractor aided mapmaking, which led some historians to name him as the device’s inventor.
However, when evidence came to light of similar tools preceding the protractor, that notion was discredited. The name of the actual inventor remains shrouded in history. After protractors became more common in the 1600s, they were regularly used by sailors and land surveyors alike. The devices began working their way into classrooms in European classrooms in the 18th century, providing all the angles for generations of geometry students.