normal to the axis of the limb and along with the area of the protrusion creates a pressure on the limb by the protrusion in a range of approximately 2 to 6 psi that displaces the intervening tissue and that then causes the stimulus electrodes to be located closer to the nerve the configuration of shaped protrusion 40 depends on the area of the electrodes to be pushed into the flesh a hemisphere half cylinder and or other shapes may be selected depending on the requirements of the size and construction of the stimulation and detection means the protrusion may be oriented in a direction relative to the electrodes so that it is non directional as in the case of a hemispherical protrusion a directional compression may be desirable if the stimulus electrodes are elongated in shape as can be achieved in the case of a half cylinder it should also be appreciated that if desired the apparatus can be used to move the detection electrodes closer to the nerve so as to improve response detection thus in one aspect of the invention there is provided a compression device for optimally stimulating a nerve to evoke a bioelectrical signal wherein the compression device comprises a spring element to create a compressive force a shaped protrusion to push aside tissue and a force indication element to facilitate tightening within a desired range whereby the predetermined relationship between the spring element shaped protrusion and resultant force has been determined by electrophysiological evoked responses in a plurality of individuals so as to augment nerve stimulation and response detection the disclosed invention provides.