Mathematics for IGCSE & O level - Geometrical Constructions (Section 3 - No. 26)
Which of the following is a key step when measuring an angle with a protractor?
Make a rough estimate of the angle.
Place the protractor so the zero line is along one of the arms of the angle.
Read the scale from the non-zero side of the protractor.
Use the scale for the side that you are using.
Explication
Key steps involve estimating, aligning the protractor, and reading the correct scale.