Ability uses an innovative dual chamber cuff to measure more reliably the systolic pressures in the ankles and is NOT based on oscillometric technology. It works on the basis of volume plethysmography and uses the distal chamber on each cuff to detect the changing volume of thelimb to measure the systolic pressures. Oscillometric devices are based on NIBP technology and were developed for the arm measurements. They have not been able to produce good results on the ankles and therefore are not very reliable in measuring ABIs. It is not clear as to which vessel the systolic pressure is measured in the ankle.