A weld gun mounted on the end of the manipulator arm of a programmable manipulator is repositioned with respect to the initially taught path in accordance with variations in the dimensions of successive workpieces on which a series of spot welds are to be made.A sensing means carried by the weld gun is employed to measure the position of the welding tips relative to the edge of the flanges which are to be welded. The output of this sensing means is employed to reposition the weld gun prior to the next weld. Repositioning may be accomplished by moving the weld gun bodily with respect to the end of the manipulator arm while the manipulator arm remains stationary at the taught position, or by modifying the command signal for the appropriate axis so that the manipulator arm is itself moved to a different position than the initially taught position.