Measuring angles with a protractor

Put the protractor's ORIGIN — the little cross or hole in the middle of its straight edge — exactly on the vertex B — not the corner of the tool.

Turn the protractor so its zero line lies along one arm.

Read the scale that starts at ZERO on that arm. There are two scales running opposite ways — use the one that reads 0 on your arm.

Check the reading against the shape before you write it: a wide-open angle cannot be 40°, and a narrow one cannot be 140°. This one is 25°.