A method that includes monitoring, by a processor of a mobile device, a stream of magnetic field measurements generated by a first sensor as the mobile device is manipulated by a user, with each magnetic field measurement representing an orientation of the mobile device relative to a reference frame. The method also includes a processor that determines a point on the surface of a magnetometer calibration sphere associated with the orientation of the mobile device, and storing the magnetic field measurement to a corresponding data bin, each data bin associated with the corresponding point on the surface of the sphere. The method continues with when the processor determining that the number of data bins containing magnetic field measurements exceeds a specified threshold, the processor triggers a magnetometer calibration process for an attached magnetometer.