An apparatus includes a detector assembly, apositioning unit, and interface circuitry. The detectorassembly includes an array of multiple magnetic fielddetectors. The positioning unit is configured to fix thedetector assembly at one or more known positions relativeto a location pad, which generates magnetic fields forperforming position measurements on an intra-body magneticfield detector using a positioning system. The interfacecircuitry is configured to output electrical signals thatare produced by the magnetic field detectors of thedetector assembly when the detector assembly is fixed atthe known positions, so as to calibrate the positionmeasurements performed by the positioning system.
