The Ability measures the systolic pressures in all 3 arteries in the ankle and reports the highest of 3. It does this by inflating the occlusion chamber over systolic pressure and then deflating this chamber while measuring the volume change in the distal (sense) chamber. The point at which the volume in the sense chamber increases is the systolic pressure.The vessel with the highest systolic pressure will start to increase the volume in the foot first. The other vessels will then contribute when the occlusion chamber drops to their systolic pressure. This way, because of physiology, we measure the highest systolic pressure reading of all 3 vessels in the ankle.