Why doctors and polygraph examiners put the blood pressure cuff on the left arm instead of the right arm

Why doctors and polygraph examiners put the blood pressure cuff on the left arm instead of the right arm:

The left arm is closer to the heart than the right arm is. The systolic (upper number) BP will be higher on your left arm because of its proximity to the pumping ventricle of the heart. For this reason it is more representative of the pressure created by the heart as it pumps, which is why the left side is preferred.