Here is an angle with a protractor beside it. Where does the protractor need to sit before you can read the angle?

Look at these angles measured on the protractor. Each time, check two things: the centre sits on the vertex, and one arm lies along a 0. Look closely at the 145° angle, both scales are showing at once, so you have to pick the ring that starts at 0 on your arm.

This last one is nearly a straight line, so the reading is easy to miss.

We work through three angles together on the board. Before each one, say which scale you would read and why, and then a pupil comes up and drags the arm so we can all check whether the class picked the right ring.