When the QRS complex is of equal magnitude in two leads, as is present here in leads I and II, the electrical axis will be between these leads, which in this example is +30 degrees. Note that the QRS complex in lead III is first positive and then negative by about the same amount. As a result, the electrical axis will be perpendicular to lead III and the line drawn form the point of intersection of the perpendiculars to leads I and II will intersect lead III at its origin.