A protractor is a hand tool that allows you to draw and measure angles. It is generally semicircular in shape, but fully circular goniometers are also available to measure 360 ° angles. Looking at this tool for the first time you might be a little confused, but don't worry, it is a very simple drawing tool to use. Once you understand which part of the protractor to use and after reading the simple steps in this article, you will quickly become a great expert in measuring angles.
Steps
Part 1 of 2: Measuring an Angle with the Protractor
Step 1. Approximate the angle measurement
Angles can be classified in three ways: acute, obtuse and right. The acute angles are narrow (less than 90 °), the obtuse angles are wider (greater than 90 °), the right angles are exactly 90 ° (two perpendicular lines). You can easily recognize them by eye. Determining what kind of angle you are going to measure first will help you identify the most appropriate scale on the protractor.
Visually, it is possible to determine that an angle is acute simply because it is less than 90 °
Step 2. Place the pointer of the protractor on the origin or vertex of the angle to be measured
Lock the protractor in place by inserting the tip of the pencil or pen into the center pointer. Rotate the protractor to align one side of the corner with the guideline on the base.
Step 3. Rotate the protractor to align one of the sides with the base
Keep the vertex of the angle at the origin and gently rotate the protractor so that one side of the angle falls on the base of the tool.
The base is parallel to the edge, but it is not the flat edge of the protractor. It is aligned to the center of the origin and the line extends on both sides from the starting point of the scale
Step 4. Follow the opposite side of the corner until you find the point where the protractor scale intersects
To obtain an accurate measurement, the side of the angle must be extended enough to exceed the outer circumference of the protractor. The number on the graduated scale at the intersection with the side of the angle indicates its amplitude in degrees. If the side of the corner does not go beyond the protractor arch, extend it using a sheet of paper. Align the side of the paper with that of the corner to create an extension that allows you to measure on the protractor scale.
- In the example shown, the angle measures 30 °. We know we need to use the smaller scale as we have previously determined that it is an acute angle. If not, we would have used the obtuse angle scale.
- Initially, the graduated scale could be a bit confusing. Almost all protractors have two opposite graduated scales, one on the inner side of the arch and one on the outer edge. This feature allows you to measure angles originating from both directions.
Part 2 of 2: Drawing a Corner Using a Protractor
Step 1. Draw a straight line
This line will correspond to one side of the angle you are going to draw and will serve as a reference for drawing the second. It is usually very easy to draw a straight horizontal line on a sheet of paper.
- To draw this line you can use the flat edge of the protractor;
- The length of the line does not matter.
Step 2. Place the protractor pointer anywhere on the line you just drew
This point will be the origin or vertex of your angle. Plot where the corner origin is.
It is not necessary to place the dot on the end of the line except for simple convenience. You can place it across the board
Step 3. Find on the scale of the instrument the number of degrees corresponding to the width of the angle you wish to draw
Align the guideline of the protractor with the straight line drawn in the first step. Draw a point on the paper at the chosen size. If you are drawing an acute angle, use the scale with the smallest numbers.
- Remember, the base is parallel to the edge, but it's not the flat edge of the protractor. It is aligned to the center of the origin and the line extends on both sides from the starting point of the scale.
- In the example shown, the angle is 40 °.
Step 4. Remove the protractor
Use a ruler, a ruler, or the base of the protractor itself to draw a line that joins the origin of the angle with the point drawn in the previous step. The second line completes the angle obtained. To verify that you have drawn the angle accurately, use the protractor to measure it.
