Human and animal AP points have electrical properties which distinguish them from surrounding skin. The electrical characteristics of the points have been well established in human cadavers and in experimental animals. The bilateral symmetry of the points has been established also. Specially adapted voltmeters or resistance meters are used to detect the points. Probe application pressure must be constant.
Readings vary with the pressure applied.
In practice, spring-loaded probes, applied at constant force, reduce this variation. Skin lesions , sweat, serum etc can greatly alter the readings. In animals the hair coat may interfere with readings. The histological reality of the points has been shown in humans and laboratory animals. Tissue around the points has more free nerve endings, vascular spirals, thickening of the epidermis and more linear alignment of collagen fibres than tissue more distant from the points.