[header] How to use a protractor [title] Approximate the measure of your angle. [step] Angles can be classified in three ways: acute, obtuse, and right. Acute angles are narrow (less than 90 degrees), obtuse angles are wide (greater than 90 degrees), and right angles are exactly 90 degrees (two lines perpendicular to each other). 
You can easily identify by eye, the category of angle you are trying to measure. Doing this step first helps you identify which scale to use on the protractor.