Introduction to the Protractor
Instructions
Background
The size of angles is measured and described in degrees. A tool for measuring angles drawn on paper is the protractor.
Step 1. Make Observations
Notice that there are two angles shown in on the GeoGebra page: angle BCA (the red angle) and angle BCD (the green angle).You can use the MOVE 
tool to move Point B, changing the size of the two angles.
Step 2. View the Protractor and Experiment
Click on the check box to show the protractor.
To make it easier to use, a protractor can measure angles from left to right or from right to left.
The outside set of degrees on the protractor measure from left to right. In this example, this is the green angle formed when you move Point B. Click on the check box to show the measurement in degrees of the green angle. You can now see the measurement in degrees of the green angle on the protractor and in the green display below the protractor. Experiment moving Point B and compare the values.
The inside set of degrees on the protractor measure from right to left. In this example, this is the red angle formed when you move Point B. Click on the check box to show the measurement in degrees of the red angle.You can now see the measurement in degrees of the red angle on the protractor and in the red display below the protractor. Experiment moving Point B and compare the values.
tool to move Point B, changing the size of the two angles.
Step 2. View the Protractor and Experiment
Click on the check box to show the protractor.
To make it easier to use, a protractor can measure angles from left to right or from right to left.
The outside set of degrees on the protractor measure from left to right. In this example, this is the green angle formed when you move Point B. Click on the check box to show the measurement in degrees of the green angle. You can now see the measurement in degrees of the green angle on the protractor and in the green display below the protractor. Experiment moving Point B and compare the values.
The inside set of degrees on the protractor measure from right to left. In this example, this is the red angle formed when you move Point B. Click on the check box to show the measurement in degrees of the red angle.You can now see the measurement in degrees of the red angle on the protractor and in the red display below the protractor. Experiment moving Point B and compare the values.