CHAPTER 3 How to Make Basic ECG Measurements This chapter continues the discussion of ECG basics introduced in Chapters 1 and 2. Here we focus on recognizing components of the ECG in order to make clinically important measurements from these time–voltage graphical recordings. STANDARDIZATION (CALIBRATION) MARK The electrocardiograph is generally calibrated such that a 1-mV signal produces a 10-mm deflection. Modern units are electronically calibrated; older ones may have a manual calibration setting. ECG as a Dynamic Heart Graph The ECG is a real-time graph of the heartbeat. The small ticks on the horizontal axis correspond to intervals of 40 ms. The vertical axis corresponds to the magnitude (voltage) of the waves/deflections (10 mm = 1 mV) As shown in Fig. 3.1, the standardization mark produced when the machine is routinely calibrated is a square (or rectangular) wave 10 mm tall, usually displayed at t...