Measurement of Magetic Field and Compass Direction

Remarks:
The mobile logger reports the magnetic field H along its three (X, Y and Z) axes in unit of mG (milligauss). Note that 1 G = 1000 mG = 10^-4 T (tesla). If there is no other magnetic substance nearby, the logger also will give the compass direction for its X axis. Otherwise, the compass direction should be interpreted as the angle between the resultant magnetic field (from Earth and nearby magnetic substances) on the XY plane and the X axis. The X and Y axes are shown in the above diagram while the Z axis is pointing vertically upwards from the surface of the logger.