Bipolar recordings utilize standard limb leads

• lead I- positive electrode on left arm, and negative electrode on right arm, and
• lead II - positive electrode on left leg and negative electrode on right arm.
• lead III - positive electrode left leg and negative electrode on left arm.

These bipolar limb leads form a triangle (heart at the center) that is - Einthoven's triangle.

these measure the potential difference between the leads. Other two limb leads, an electrode on serves as a reference electrode for recording purposes.