A protractor is usually a transparent measuring device laid intended to be laid over an angle to be measured. The centerpoint of the protractor's scale is made to coincide with the angle's vertex, and the baseline of the protractor is aligned with one of the angle's rays. The appropriate scale is used to read the angle where the other ray crosses the scale. You usually have to visually determine if the angle is acute or obtuse, so you can choose the correct scale to read.

If you're drawing an angle, first draw one ray and locate the vertex on it. Then do the steps above as you would for measurement. Make a mark on your paper corresponding to the desired angle measure, and connect the vertex to that mark to create the other ray of the angle.

If you're working with a printed protractor, you may need to do your work on a piece of translucent paper or transparency material, so you can see the protractor scale through the page you're drawing on.

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Comment on a printed protractor

A protractor will only give accurate measurements if its geometry is perfect. Some printers will scale a figure differently in horizontal and vertical directions, so will make the protractor scale be elliptical instead of circular. That will give wrong readings.

7 0

3 years ago