A mobile electronic device for a headset including a holder configured to releasably retain the mobile electronic device in a defined pose relative to the headset, the mobile electronic device comprising: a camera configured to output digital pictures and arranged by the holder to view a portion of the headset; a display device arranged by the holder to display information for viewing by a user wearing the headset; a processor operationally connected to the camera and to the display device; and a memory storing program code that is executed by the processor to perform operations comprising: retrieving calibration parameters from the memory that characterize at least a pose of the camera relative to the display device; processing a digital picture from the camera to identify a pose of an optically identifiable feature of the headset within the digital picture that was captured by the camera while the mobile electronic device is retained by the holder; identifying a pose of the mobile electronic device relative to the holder based on the identified pose of the optically identifiable feature of the headset within the digital picture and based on at least the pose of the camera relative to the display device as characterized by the calibration parameters; and controlling where graphical objects are rendered on the display device based on the identified pose of the mobile electronic device relative to the holder. a camera configured to output digital pictures and arranged by the holder to view a portion of the headset; a display device arranged by the holder to display information for viewing by a user wearing the headset; a processor operationally connected to the camera and to the display device; and a memory storing program code that is executed by the processor to perform operations comprising: retrieving calibration parameters from the memory that characterize at least a pose of the camera relative to the display device; processing a digital picture from the camera to identify a pose of an optically identifiable feature of the headset within the digital picture that was captured by the camera while the mobile electronic device is retained by the holder; identifying a pose of the mobile electronic device relative to the holder based on the identified pose of the optically identifiable feature of the headset within the digital picture and based on at least the pose of the camera relative to the display device as characterized by the calibration parameters; and controlling where graphical objects are rendered on the display device based on the identified pose of the mobile electronic device relative to the holder. retrieving calibration parameters from the memory that characterize at least a pose of the camera relative to the display device; processing a digital picture from the camera to identify a pose of an optically identifiable feature of the headset within the digital picture that was captured by the camera while the mobile electronic device is retained by the holder; identifying a pose of the mobile electronic device relative to the holder based on the identified pose of the optically identifiable feature of the headset within the digital picture and based on at least the pose of the camera relative to the display device as characterized by the calibration parameters; and controlling where graphical objects are rendered on the display device based on the identified pose of the mobile electronic device relative to the holder. <EOS>