Obtain an ECG readout of the patient with at least two of the bipolar leads on it as well as the reference axes.
Focus on the QRS complex of the ECG; it contains the ventricular depolarization. Look for the QRS complexes in each lead. The leads include the isoelectric line which is the zero current flat line, the R wave, which is positive current, and and S wave which is negative current.
Count from the isoelectric line to the top and bottom of the R and S waves to determine the difference for each wave. Each square on the ECG will represent a millimeter (mm).
Subtract the different of the two heights. So if the R wave is 5 mm, and the S wave is 2 mm, then the result is 3 mm.
Plot this new point (3 mm) on a graph to complete the calculation.