In the ECG strip on page 49 (“Method 3: ECG Test Strip Heart Rate Calculation”) measure the R-R intervals where there is no block. They are regular and sinus in origin (see the normal P waves). This is called the underlying rhythm: the regular rhythm that continues across the ECG strip. Notice the underlying rhythm (R-R intervals) without the block is sinus at 75 bpm. You should use Method 2: Precise Heart Rate Calculation for this measurement since it is the most accurate. The calculation would be 1,500/20 = 75 or 75 bpm. The heart rate (or bpm) of the underlying rhythm (if there is one) should be included in the heart rate measurement.