Every physician prescribing TENS units should have exact information on the technical details of the devices. Data on current (at a load of 3 kOhm, not less!) have to be supplemented by duration of a single impulse (200 µsec or less). One should use devices only if they provide electrodes of very unequal sizes. See section K of appendix. The shape of impulses should be monophasic square waves; biphasic impulses or asymmetrically biphasic impulses should not be prescribed. Every unit should be provided with a scheme of sensory distribution for allowing marking of electrode positions. Use red pencil for anodal and blue color for cathodal positions. Also mark these positions on the skin of patients! The skin mark should be renewed if the color disappears. Examples of sensory schemes are given under section J in the appendix.