Page 2 - CH - 2 - LN - 2.4

Measuring angles is a fundamental concept in geometry, and to do this accurately, we use a tool
called a protractor. A protractor is either a full circle divided into 360 equal parts or a half-circle
divided into 180 equal parts.

Using a Protractor

 Protractor Structure: A typical protractor has a straight angle at the center, divided into 180
units of 1 degree each. These units help you measure angles precisely.

 Reading the Protractor: Starting from the rightmost point, there are long marks for every 10
degrees and medium-sized marks for every 5 degrees. This makes it easier to count and
measure angles.
There are two types:

 Unlabelled Protractor: A protractor without numbers, showing only marks. You count the
degree units from the markings to measure an angle. This requires you to carefully count
each small mark to determine the angle.

 Labelled Protractor: A protractor with numbers marked, making it easier to measure angles.
The numbers typically range from 0° to 180° in both directions (clockwise and
counterclockwise).

Using a labelled protractor simplifies the process of measuring angles, as you can directly see the
angle's degree measure.

Measuring Angles with a Protractor

1. Place the Protractor: Align the protractor so that its center is on the vertex of the angle.