How to Use a Full Circle Protractor

Though not as popular as its half-sibling, the semi-circle protractor, the full circle protractor benefits from using all 360 degrees of a circle's circumference for measurement purposes. The full circle protractor mimics the essential shape of the geometric shape, allowing for more straightforward measurement recording. Using a full circle protractor can help you to size angles and also help you understand how those angles relate to the circle in general.

• 1

  Align the longer edge of the middle bar of the protractor with the lower line of the angle. The middle bar will either have a longer lower or upper edge, or it will have edges of the same length. If the edges are the same length, align the lower line of the angle with the line drawn on the middle bar (the material used will be transparent). The upper line of the angle should be partly or wholly underneath the middle bar, depending on the size of the angle.

• 2

  Align the dash in the middle bar with the intersection point of the angles. The upper line of the angle should reach one of the degree measurements written on the edge of the protractor. If it doesn't reach, use the straight edge of the protractor to extend it, and then start the process over from the beginning.

• 3

  Write down the top measurement as the measurement of the angle if there are two measurements. The top, and lesser measurement is for the smaller angle. Write down the bottom, or larger measurement for the angle's reflex angle, which is the angle subtracted from 360 degrees.