A magnetometer is a sensor that is similar to a compass. A compass detects the horizontal component of the direction of a magnetic field. Magnetometers detect both the directional components and the strength of a magnetic field.
Magnetometers in BlackBerry® devices are calibrated to sense the magentic field of the earth. They are designed to measure and remove interference caused by local magnetic fields so that only the magentic field of the earth is measured. You can test the calibration quality of a magnetometer and trigger a new calibration when necessary.
An obvious use of a magnetometer is to create a digital compass by creating a UI that presents the directional magnetometer data. Because a magnetometer includes additonal information about the magnetic field, such as the field strength, you can use it for many other purposes. For example, magnetometers are used in metal detectors, geological exploration tools, stud and pipe finders, and applications that require precise inclination measurements.