Inside magnetometers, charged particles interact with the external magnetic field, which comes from Earth's interior and from the sun, in ways that make it possible to measure that field's strength and direction. Magnetometers are thus entirely passive devices. AWI uses a variety of magnetometers to measure the magnetic field strength and direction. For static measurements on the ground, the institute uses several GEM Systems proton precession magnetometers that can be set up to measure continuously for days or weeks unattended. On Polarstern, two fluxgate three-component magnetometers are mounted on the crow's nest where they continuously record the magnetic field strength in three orthogonal directions. These measurements need to be corrected for the localised influence on the field strength caused by the shape and movement of the magnetically-susceptible parts of the ship and its cargo in Earth's main magnetic field. This is done using custom-written software after completing precise circular manouevres at various points during a science cruise. Polarstern also acts as a base for two helicopters, either of which can be set up to tow a Scintrex Caesium vapour magnetometer in a streamlined 'bird' at the end of a 40 m long communication cable. This greatly enhances the ship's magnetic survey capability. Polar 5 and 6 can be configured with as many as three magnetometer devices. A three-component fluxgate magnetometer in the aircraft's fuselage serves to record the local field as deformed by the moving magnetically-susceptible aircraft. One or two Scintrex Caesium vapour magnetometers can be mounted in nose and/or tail booms where the effect of this deformation is minor and can be compensated for using the measurements of the fluxgate device.