Abstract: A seam tracker in which a shaft containing a position-indicator-member, e.g., a ferromagnetic portion, is attached to a probe, and is mounted on a ball joint and the ball joint is pivotally mounted on a pin the ends of which extend through slots in a housing. Spring means urge the pin ends against one end of the respective slots. A mechanical null position spring urges the shaft to a mechanical null position off of the longitudinal axis of the housing. A means responsive to changes in position of the shaft from an electrical null position along the longitudinal axis of the housing gives an output to drive a control apparatus to correspond to changes in position of the probe represented by changes in position of the shaft.