= GeoMagnetism =
 . https://www.ngdc.noaa.gov/geomag/faqgeom.shtml#Is_Earths_magnetic_field_going_to_reverse
 . https://maps.ngdc.noaa.gov/viewers/historical_declination/
 . https://www.ngdc.noaa.gov/IAGA/vmod/igrfhw.html

 . [[ http://www.geophysik.uni-bremen.de/statisch/downloads/254/Overhauser-Magnetometers.pdf | Magnetometer pdf ]]  [[ attachment:Overhauser-Magnetometers.pdf | local copy ]]