Rationale: A systematic approach to interpreting each strip is needed for consistency. Rate refers to frequency, determined by spaces between R and R. Rhythm is the interval of the pattern between R waves. The P wave is produced when the left and right atria depolarize. Regular intervals vary by less than 0.06 seconds. The P wave should occur regularly; be one for every QRS complex; be smooth, rounded, and upright in appearance; and look similar. The P-R interval measures the time from the onset of atrial contraction to onset of ventricular contraction. The normal interval is 0.12 – 0.20 seconds. The QRS complex presents depolarization (contraction) of the ventricles. The normal interval is 0.06 – 0.12 seconds.