The RSU Rotation Sensor Unit is designed in order to measure the relative or absolute rotation angle of a rotating turret on a mobile machine , such as excavators , cranes or access platforms . Where the rotation is not mechanical limited The particularity of this sensor is that the measured angle is not related to a mechanical displacement between the turret and the chassis of the machine , but with respect an absolute direction angle . In order to obtain such a feature , a multi-axis magnetometer device is used . The operating principle is then based upon the detection of the earth magnetic field variation according to the orientation of the device in the horizontal plane. In order to compensate the magnetic offsets caused by the huge magnetic masses of such kind of machines , a calibration procedure , executed by means of a microcontroller located on a main board , is able to calculate the offsets of the magnetic field caused by the iron mass and then store the resultant values on the magnetometer handling processor memory .