With the magnetic field measurement we survey the low-frequency range from 0 to 300 Hz. This is called "B-0 measurement", and only magnetic fields in the AC and DC-range get measured. Mostly these magnetic fields are caused by high energy fluxes, known sources for that are transformer stations, high voltage paths, trams, railroads and underground trains. As further sources for magnetic field fluctuations, we can account big movable ferromagnetic masses near a MRI-ISO-center – for example elevators, heavily trafficked streets or parking lots. With the measurement we can determine how big the magnetic exposure is, since every MR-tomograph got his own exact specifications. By reference to the measurement data we can provide, which arrangements have to be done to fulfil these specifications. But there are more regulations in addition, for example for the personal protection. Special clients as these with pacemakers, insulin pumps and further should not be affected. To ensure this, we also provide the so-called "5-Gauss-line-survey" during a MF-measurement.