Figure 4-29:
Bailey's hexaxial reference system. The lead axes are marked in 30-degree increments from 0 to 180 degrees and from 0 to −180 degrees. The six leads are marked with a plus sign at the positive electrode and a minus sign at the negative electrode. Note that in the leads I, II, III, and aVF the polarity and the angle of the leads are positive or negative simultaneously. Leads aVF and aVL are positive at the positions of −150 degrees and −30 degrees, respectively, because the positive electrodes for those leads lie in the negative 0- to −180-degree zone.
(From Ettinger SJ, Suter PF: Canine cardiology, Philadelphia, 1970, WB Saunders.)