We use both half-circle protractors and whole-circle protractors.
If the rays are not long enough, use the straightedge of the protractor to make the rays longer.
Be extremely careful to line up the vertex in the hole, and one of the rays along the 0-degree mark.
Always decide what kind of angle you have before you measure it. An acute angle is always less than 90 degrees, an obtuse angle is always between 90 and 180 degrees, and a reflex angle is always between 180 and 360 degrees.
Make an estimate before you measure.
After measuring, always check that your measurement makes sense. When you measure an angle with a protractor, you’ll have to choose to use a higher number or a lower number. Make sure you choose the correct measurement for the type of angle you have.