The wobble of Earth’s axis is called precession. While most of us are familiar with our planet’s primary motions — rotation and revolution — few are aware of precession. This characteristic is vividly ...

In a “normal” electrocardiogram (ECG), the transition of the QRS axis in the precordial leads occurs between leads V 3 and V 4 (i.e., there is a dominant S in V 3 and a dominant R in V 4).