The Earth’s magnetic field changes continuously and behaves differently depending on where it is measured. The Earth’s magnetic field is a vector quantity, and therefore three components (X- north, Y- east, Z- vertical) need to be measured in order to fully define its intensity and direction.

Geomagnetic observatories record the Earth’s magnetic field and are collaborating together through the worldwide network Intermagnet.

A geomagnetic observatory needs several instruments to perform these measurements. Aside a "variometer" measuring XYZ variations of the Earth’s magnetic field, two instruments are used to calibrate these variometer measurements: an Overhauser magnetometer for intensity, and a DIflux instrument for the direction (Declination and Inclination). RMI has a long-standing experience and a worldwide reputation for its range of DIflux instruments.