Place the origin of the protractor over the vertex of the angle to be measured. The protractor's origin may be marked with a dot, a hole, or cross-hairs. The vertex of an angle is the point where the two lines meet to create the angle.
Rotate the protractor until the baseline of the protractor lies over either one of the two lines forming the angle. Ensure that the origin remains centered over the vertex of the angle. The baseline of the protractor is the straight line joining the 0-degree and the 180-degree markings on the protractor. The degree-markings are found along the curved edge of protractor. The baseline is equivalent to 0 degrees.
Read the angle at which the second line of the angle intersects the curved edge of the protractor. Be careful to use the correct scale when taking this reading, as the protractor has a clockwise and an anticlockwise scale. The choice of scale is determined by position of the first line. Always read from the first line (set at 0 degrees) to the position of the second line. For example, consider a case where the first line is aligned with the protractor baseline and the second line crosses the protractor edge at 149 degrees on the one scale and 31 degrees on the other scale. Find the 0-degree marking on the protractor that aligns with the first line, and follow the scale from 0 degrees to the second line. The correct angular reading is the one on the same scale as the 0-degree starting point.