Definition of Angle explained with real life illustrated examples. x = 19, the measure of angle ABC = 4(19) - 12 = 64. Step 2: Adjust the base line of the protractor so that it is aligned with the line BC Step 3: Read the value of angle ABC, from the inner scale. In 'abc' your endpoints are a and c. Try to imagine it as ">" where the top end of that is A, the vertex being B and the bottom end is C. You need to be careful when identifying these types of angles, because they can look like acute or obtuse angles. There is the original $\angle ABC$ which measures 60$^\circ$. However, to avoid confusion, that is why it's called