A tester uses to test the function of T.E.N.S. unit. Simply insert the pin leads from T.E.N.S. unit into the socket of the tester and turn on the T.E.N.S.unit, if the pilot light of the tester blinks same as the T.E.N.S. Unit means that the T.E.N.S. unit is functioning well. This tester helps people to test the function of the T.E.N.S. before sending back the T.E.N.S. unit for repair.