![]() Make a mark on the paper as close as possible to the tick mark.įinally, complete the line by connecting the vertex and the angle mark you just added using the straight edge of the protractor or a ruler. The next step is to locate the tick mark corresponding to either the obtuse or acute angle you wish to draw. Now, align the origin of the protractor with the vertex on the line, then align the base line of the angle with the line on the bottom of the protractor. Step 3: Align the Protractor on the Vertex Next, draw the vertex of the angle at the end of the line. This is the base line or arm of the angle The first step is to draw a straight line on a sheet of paper using the straight edge. ![]() Protractors are also great for drawing accurate angles. The measurements should be incrementing in the direction you are measuring. ![]() There are two rows of tick marks on a protractor to allow measuring the degrees of angle from either the left or right. If the acute angle is on the right then the tick mark will be on the inside of the curve. If the acute angle is on the left the tick mark will be on the outside, or outer-most edge, of the protractor. With the origin of the protractor aligned over the vertex of the angle and the horizontal edge aligned with one of the lines, find the tick mark along the curve where the line meets. If a line were to meet another line forming two angles, the acute angle would be the smaller angle. Īn acute angle is the smaller angle where a line meets another, or technically any angle that is less than 90°.Īn obtuse angle is the larger angle where a line meets another, or technically any angle that is more than 90°.Ī right angle is an angle that is exactly 90°, which means that the two lines are exactly perpendicular to each other. The digitization of this group of artifacts was made possible through the generous support of Edward and Diane Straker.There are three types of angles that you can find using a protractor: acute, obtuse, and right. Although there are not many academic books and articles specifically devoted to the protractor, the page of resources offers suggestions for further learning about the general history of drawing instruments. They were made in Italy, France, England, the United States, Switzerland, Germany, and Japan. These five-dozen examples also represent dates from about 1700 to 2000. Hart Combination Protractor, Rule, And Square, ca 1925Īs you will see by browsing through the images on the following pages, this diversity of shapes, sizes, and materials is reflected in the NMAH mathematics collections. They may be made of brass, steel, wood, ivory, or plastic. 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. Protractors are mathematical drawing instruments used to draw and to measure angles. ![]()
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