In the 1940s, Dr. Goldberger observed that the voltage signal recorded by the unipolar limb leads could be augmented by omitting from the central terminal that connection originating on the extremity being explored and by removing the 5,000 ohm resistors. Thus in lead aVR, the positive lead is the right arm lead and the indifferent, or reference lead is the combined output of the left arm and left leg leads.