The Fluxgate Magnetometers (FGM) on Magnetospheric Multiscale consist of a traditional Analog
Fluxgate Magnetometer (AFG), and a Digital Fluxgate magnetometer (DFG). The dual magnetometers are operated as a single
instrument providing a single intercalibrated data product. Range changes occur at different times on the two instruments
so the gains checked each periapsis can be carried out unambiguously to apoapsis. Cross correlation of calibration
parameters can separate causes of the any apparent calibration changes. Use of Electron Drift Instrument (EDI) to determine the field along the
rotation axis allows accurate monitoring of the zero levels along the rotation axis. Prior to
launch the magnetometers were calibrated at the Technical University, Braunschweig, except for the AFG magnetometers on MMS3 and MMS4,
which were calibrated at UCLA. Both sets of sensors are operated for the entire MMS orbit, with slow
survey (8 samples per second) outside of the Region of Interest (ROI), and fast survey (16 samples per second) inside the ROI.
Within the ROI burst mode data (128 samples per second) are also acquired.