Cardiologists use calipers. Intensivists write little marks on a page and march them across. Emergency providers fold the ECG in half and hold it up to the light. Or the sun. Fold the tracing in half. Hold up to the light. Now align the QRS complexes. The rhythm is regular. Here is another example. Irregular. Cannot line up QRS complexes.
by reuben in arrhythmia, ecg