Drawing angles is a skill required in many situations, from school lessons through to working as a cartographer or rocket engineer. Although it is possible to draw many angles with a compass, it is not the only tool available. A semicircular protractor is a useful tool for measuring and drawing angles not exceeding 180 degrees. A protractor has an outer edge marked in degrees, from zero to 180, and a horizontal baseline and vertical centerline to facilitate accurate positioning. Using a protractor is simple.
Draw a horizontal line using the flat base of the protractor. Draw a short vertical line crossing the horizontal one near the left-hand end of the line. This provides a guide for positioning the protractor in Step 2.
Rest the protractor over the horizontal line. Ensure that the protractor baseline -- joining zero degrees and 180 degrees -- is exactly on top of the line, and that the vertical line in the centre of the protractor base aligns with the vertical guideline drawn in Step 1.
Locate the 45-degree mark on the curved perimeter of the protractor and make a small pencil mark on the drawing surface.
Move the protractor and use the straight base to draw a line between the guide mark on the horizontal line and the mark representing 45 degrees. The angle between the two lines is 45 degrees.
Use a semicircular protractor to measure any angle between zero and 180 degrees. Full circle protractors enable any angle to be drawn. Some drafting triangles have 45-degree corners.
Blunt and wide-tipped pencils reduce the accuracy of measurements. Always use a sharp pencil.
Tips and warnings
- Use a semicircular protractor to measure any angle between zero and 180 degrees.
- Full circle protractors enable any angle to be drawn.
- Some drafting triangles have 45-degree corners.
- Blunt and wide-tipped pencils reduce the accuracy of measurements. Always use a sharp pencil.
Things you need
- New Mexico State University - College of Arts and Sciences: Angles and Angular Measurement
- OpenLearn: LabSpace: How To Measure an Angle
- Georgia State University Astronomy Program: Angles and Scales
- Math Is Fun: Using a Protractor
- Southern Polytechnic State University Department of Mechanical Engineering Technology ; Chapter 6 Technical Drawing Tools; Simin Nserias
- Washington State University Program in Astronomy; Determination of the Orbit of Mercury; Michael Allen