A method and apparatus for determining a position of an external transceiver (24) relative to an implanted transceiver (23) comprising means (30) for measuring the strength of a magnetic field proximal to the external transceiver (24) and means for determining a position of the external transceiver (24) relative to the implanted transceiver (23) from said measured magnetic field strength. Furthermore there is disclosed is a method and apparatus for determining a skin flap thickness of a recipient of a prosthesis including a transcutaneous link between the external transceiver (24) and the implanted transceiver (23). A skin-flap thickness meter is also provided.
