The HeartSine 500P uses an Impedance Cardiogram (ICG) to assess how good the CPR is - are the compressions fast enough? Hard enough? The Impedance Cardiogram (ICG) measure impedance changes in blood volume in the chest cavity which determines effective CPR. Since the blood flow is related to how fast the compressions are applied as well as how hard, the 500P can guide you on both. Includes leather case complete with adult pads and battery. For all ages and abilities. Semi and professional life saver.