The perpendiculars to lead I and lead III at the 1.1 mm and 0.9 mm positive positions respectively on the lead axes intersect at a point which is just superior and slightly to the the left of the lead II axis. A perpendicular from this point to the lead II axis will intersect it at 2 mm, the amplitude of the P wave in lead II. A line extended from the intersection point of the of the 3 perpendiculars to the origin of the triaxial system defines the electrical axis of the P wave in the frontal plane, which, in this example, is -59 degrees. Lines drawn perpendicular from this intersection point to the axes of the augmented leads (aVR, aVL, and aVF) will allow prediction of the P wave amplitude in these leads.