An angle is measured by using a protractor. The parts of a protractor are shown here. We have a baseline, a center point, and two scales of degrees. Let’s now look at how we use the protractor to measure an angle’s size in degrees. We’re going to measure this angle.
Do you remember the names of the angles? Which type is this? Well done if you said acute. Now let’s measure it. We place the protractor over the angle, as shown. It’s important to line up the baseline on one of the rays, and by baseline, I mean the line drawn through zero, not the bottom edge of the protractor. Now, place the center point of the baseline on the vertex of the angle. Then we just follow the other ray outwards to the scale on the outside edge of the protractor, and we can see that there are two measurements, 70 degrees and 110 degrees.
It’s important to recognize that we have to measure using the scale that reads zero on the other ray of the angle. So, the measurement we need here is 70 degrees. 110 degrees would be the measurement if the first ray of the angle was on the other side, over here. You can see that this angle is less than a right angle, or 90 degrees, so that’s another hint as to which angle measurement to use.
