A system and method for determining depth of compressions of a chest of a patient receiving chest compressions or cardiopulmonary resuscitation (CPR) A field, such as an electromagnetic field, is generated by a field generator which is stationary relative to the patient and detected by a compound field detector moving with the chest of the patient The compound field detector includes at least two coils at a fixed distance and is adapted to generate a response signal indicative of at least one of the at least two coils detecting the field.