An apparatus includes a detector assembly, a positioning unit, and interface circuitry. The detector assembly includes an array of multiple magnetic field detectors. The positioning unit is configured to fix the detector assembly at one or more known positions relative to a location pad, which generates magnetic fields for performing position measurements on an intra-body magnetic field detector using a positioning system. The interface circuitry is configured to output electrical signals that are produced by the magnetic field detectors of the detector assembly when the detector assembly is fixed at the known positions, so as to calibrate the position measurements performed by the positioning system.
