This Ultima 20 unit comes with five mode device with dual channels, three wave forms, and 20 treatment modes. It is remarkable for its body part specific settings for ease of application and set-up by the patients. T.E.N.S. works by stimulating your body's own natural defenses against pain. The unit produces a gentle stimulation through pads normally placed over the area of pain. This stimulus helps the body to produce natural pain relievers called endorphins. The correct positioning of the pads is important. Some people feel immediate benefit from T.E.N.S. However, some may only achieve benefit after repeated treatment sessions and over an extended period of time.