In some diagrams, you may see more than one angle. The arc around the vertex shows you which angle you’re supposed to find the value of. Labeling an angle acute or obtuse helps you reading the protractor. For example, if you know you have an obtuse angle, then you know it is going to be more than 90 degrees. If you get a smaller number from your protractor, you’re likely looking at the wrong scale.
To make sure you’re right on the vertex, it can help to make a little dot inside the center of your protractor. Then remove your protractor and confirm the dot is on the exact tip of the vertex.
If one line is more horizontal, it will typically be the easiest one to line up along the baseline. However, you’ll get the same result no matter which line you use. [5] X Research source
Protractors usually provide numbers in 10s. If the angle you’re measuring doesn’t line up perfectly with a number, count the hash marks on the outside edge of the protractor to determine the degrees in that angle.
If you look below the straight line, you’ll see another angle. This smaller acute angle is formed by the straight line you drew and the diagonal line of the original reflex angle.
You may find it easier to measure if you turn your paper so that the acute angle is facing straight up.
For example, if the reflex angle produces an acute angle of 18 degrees, that would mean the reflex angle is 198 degrees.
