In general, the invention relates to an algorithm and process for automated and/or continuous calibration of magnetic sensor, for example such as a sensor installed in a mobile positioning system handset. According to certain aspects, the calibration process can use the normal motion of the handset such that all measurement data from the three orthogonal axes of sensor when exposed to Earth's magnetic field is collected. According to still further aspects, the process includes fitting measurement data to an ellipsoid that characterizes the actual magnetic field measurements from a magnetic sensor, so that anomalies such as hard iron effect, soft iron effect and scale factors can be extracted and/or corrected by comparison to a sphere represented by magnetic field data from a model at the sensor's location.