Step 3b: Calculate the electrical axis
The mean QRS axis is oriented towards the lead with the greatest net QRS deflection. To calculate the net QRS deflection, add up the number of small squares that correspond to the height of the R wave (positive deflection), and subtract the number of small squares that correspond to the height of the Q and S waves (negative deflection).

In actual fact, the net QRS deflection can be approximated without resorting to counting squares. In the example shown here, one can easily see that the net deflection is slightly more positive than negative. 