The program asks whether you are supplying geodetic or geocentric latitude and longitude. The 'usual' values defining positions on the Earth's surface are geodetic coordinates. If you specify geodetic coordinates then the height in kilometres above sea-level is also required. If you specify geocentric coordinates then the geocentric distance in kilometres is required. The input parameters are listed to enable you to check that they were entered correctly.
Declination is positive if magnetic north is east of true north.
The north component of the field e. The total intensity of the field The latest version of the IGRF program is now available and is the program in use on this service.