Methods and devices for detecting magnetic interference affecting the operation of a magnetometer

Methods and apparatus employing non-magnetometer navigational sensor data to assist in determining whether a change in a magnetic field detected by a magnetometer is likely due to a source of internal or external magnetic interference, and more generally, whether such interference is likely to be persistent or transient. If the magnetic field data detected by the magnetometer indicates a large change in magnetic field, but the non-magnetometer navigational sensor (e.g., gyroscope) data does not indicate a corresponding change in orientation of the mobile device contemporaneous with the change in magnetic field, then the cause of the magnetic field change may be determined as likely originating from a localized external interference source and the device may prompt the user to move away from the interference source, rather than initiating a recalibration of the magnetometer.