1. A resistance welder for joining a plurality of parts, said spot welder comprising: an electrode electrically coupled to a weld controller; a cylinder assembly having a cylinder housing, a piston and piston rod attached thereto for linearly displacing said electrode; a transducer for detecting the displacement of said electrode relative to the cylinder housing and generating a displacement signal responsive thereto; and a microprocessor controlled monitor cooperating with the weld controller for evaluating the displacement signal occurring during each cylinder movement to determine proper part fit up and to compensate for electrode wear prior to the initiation of welding, for monitoring real time displacement of the electrode as a result of welding, in order to cooperate with the weld controller to vary weld duration responsive to the electrode displacement, for monitoring weld expulsion and for providing an indication in response to said weld expulsion.