If you are getting unexpected or unusual readings from the Magnetic Field Sensor, first confirm that the range setting is appropriate for the experiment. The ±6.4 mT range is used to measure relatively strong magnetic fields around permanent magnets and electromagnets; the ±0.32 mT range is used to measure the magnetic field of the Earth and very weak fields. If you are using the ±0.32 mT range for investigating permanent magnets, make sure that the sensor remains in one position so that the reading is not affected by the background field of the Earth.