Measuring Angles

2.9 Degrees

To measure angles precisely, we use a unit called a degree ($^\circ$). Imagine a full circle (one full turn) divided into 360 equal parts.

• 1 Full Turn = $360^\circ$
• Straight Angle (half turn) = $180^\circ$
• Right Angle (quarter turn) = $90^\circ$

Using a Protractor

A protractor is a geometric tool shaped like a semicircle, divided into 180 equal parts (degrees).

Reading a Protractor

Most protractors have two scales:

1. Inner Scale: Usually counts $0^\circ$ to $180^\circ$ from Right to Left (Counter-Clockwise).
2. Outer Scale: Usually counts $0^\circ$ to $180^\circ$ from Left to Right (Clockwise).

How to Measure

1. Place the center point of the protractor on the vertex of the angle.
2. Align the baseline (the $0^\circ$ line) with one arm of the angle.
3. Read the value where the other arm crosses the scale.
   • Tip: Look at the $0^\circ$ mark you started with. If you used the $0^\circ$ on the right, read the inner scale. If you used the $0^\circ$ on the left, read the outer scale.