we have to take the measure of inner scale or outer scale?????????

### Measuring Angles

A **protractor** is used to measure angles. In this section, we will consider the use of a protractor that has the shape of a semi-circle and two scales marked from 0º to 180º.

The two scales make it easy for us to measure angles facing different ways.

To measure the size of angle *ABC*, place the protractor over the angle so that the centre of the protractor is directly over the angle's vertex, B; and the base line of the protractor is along the arm, *BA*, of the angle.

We use the inner scale to measure the angle *ABC*, as the arm *AB* passes through the **zero **of the** inner** **scale**. Following the inner scale around the protractor, we find that the other arm, *BC*, passes through the inner scale at 60º. So, the size of angle *ABC* is 60 degrees. We write this as follows:

To measure the size of angle *PQR*, place the protractor over the angle so that the centre of the protractor is directly over the angle's vertex, *Q*; and the base line of the protractor is along the arm, *PQ*, of the angle.

We use the outer scale to measure the angle *PQR*, as the arm *PQ* passes through the **zero **of the** outer** **scale**. Following the outer scale around the protractor, we find that the other arm, *QR*, passes through the outer scale at 120º. So, the size of angle *PQR *is 120 degrees. We write this as follows:

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