A device for the determination of at least one compression parameter during administration of cardiopulmonary resuscitation on a patient comprising: a first defibrillator pad configured to be located on the patient's chest, the first defibrillator pad comprising a reference sensor, the reference sensor including a field generator adapted to generate a field; a second defibrillator pad configured to be located on the patient's chest, the second defibrillator pad comprising a position sensor, the position sensor including a field detector adapted to move in accordance with the patient's chest to detect the field generated by the field generator and generate a response signal; and a processor adapted to determine from the response signal position information for the field detector relative to the field generator, including calculating position and orientation information of the position sensor, and to determine the at least one compression parameter using the determined position information of the field detector, the at least one compression parameter including a compression angle, the compression angle calculated based on the calculated position and orientation information, and to determine whether a rescuer is administering CPR at a desired angle to the patient's chest; wherein the first defibrillator pad is configured such that at least a portion of the first defibrillator pad remains substantially stationary relative to the position sensor of the second defibrillator pad, the portion comprising the reference sensor such that the reference sensor remains substantially stationary relative to the position sensor, wherein the field generator comprises three orthogonally wound field generating coils and the field detector comprises three orthogonally wound field detecting coils, and the generated field is an electromagnetic field, wherein the processor is provided in a base unit, and the position sensor and the reference sensor are configured to be in communication with the base unit, and wherein the position sensor contains a wireless signal transmitter for sending at least one of a synchronization signal and the response signal to the base unit, the synchronization signal being used in determining the position information. a first defibrillator pad configured to be located on the patient's chest, the first defibrillator pad comprising a reference sensor, the reference sensor including a field generator adapted to generate a field; a second defibrillator pad configured to be located on the patient's chest, the second defibrillator pad comprising a position sensor, the position sensor including a field detector adapted to move in accordance with the patient's chest to detect the field generated by the field generator and generate a response signal; and a processor adapted to determine from the response signal position information for the field detector relative to the field generator, including calculating position and orientation information of the position sensor, and to determine the at least one compression parameter using the determined position information of the field detector, the at least one compression parameter including a compression angle, the compression angle calculated based on the calculated position and orientation information, and to determine whether a rescuer is administering CPR at a desired angle to the patient's chest; wherein the first defibrillator pad is configured such that at least a portion of the first defibrillator pad remains substantially stationary relative to the position sensor of the second defibrillator pad, the portion comprising the reference sensor such that the reference sensor remains substantially stationary relative to the position sensor, wherein the field generator comprises three orthogonally wound field generating coils and the field detector comprises three orthogonally wound field detecting coils, and the generated field is an electromagnetic field, wherein the processor is provided in a base unit, and the position sensor and the reference sensor are configured to be in communication with the base unit, and wherein the position sensor contains a wireless signal transmitter for sending at least one of a synchronization signal and the response signal to the base unit, the synchronization signal being used in determining the position information.