Angles are measured using a protractor. A protractor measures in degrees. A protractor is normally a semi-circle (as found in geometry sets) or a complete circle.
There are four basic steps to measuring an angle accurately using a protractor.
1. Place the centre of the protractor (the middle of the bottom line, normally shown with a circle) exactly on the point of the angle being measured:
2. Make sure that the base line of the protractor is exactly on top of one of the lines of the angle:
3. Check if the inner scale (of numbers) or the outer scale is being used by determining which scale is at 0º on the line:
4. Read the angle measurement from the correct (inner or outer) scale:
In this instance, the angle being measured is 42º
1. What is the size of the angle being measured below?
The zero is on the inner scale. Reading from the zero, read an angle of 55º.
2. What is the size of the angle being measured, below?
The zero is on the outer scale. Read round the outer scale to 132º.