Declination is the angle of difference between true North and magnetic North. For instance, if the declination at a certain point were 10° W, then a compass at that location pointing north (magnetic) would actually align 10° W of true North. True North would be 10° E relative to the magnetic North direction given by the compass. Declination varies with location and slowly changes in time. See the Geomagnetic FAQ page for more information.

At a given location, the Inclination is the angle between the magnetic field vector and the horizontal plane (the plane is tangent to the surface of the Earth at that point). The inclination is positive when the magnetic field points downward into the earth and negative when it points upward. See the Geomagnetic FAQ page for more information.

The horizontal intensity is the intensity of the component of the magnetic field is tangent to the Earth surface at a given point. See the Geomagnetic FAQ page for more information.

The North component is the portion of the magnetic field that is directed horizontally northward. A southward directed field would have a negative value for the North component. See the Geomagnetic FAQ page for more information.

The East component is the portion of the magnetic field that is directed horizontally eastward. A westward directed magnetic field has a negative value for the East component. See the Geomagnetic FAQ page for more information.

The vertical component is the portion of the magnetic field that is directed perpendicular to the Earth's surface at a given location. Down is measured as positive and up as negative. See the Geomagnetic FAQ page for more information.

The total field is the intensity (or strength) of the entire magnetic field at a given location. Geometrically, it is the length of the magnetic field vector. See the Geomagnetic FAQ page for more information.

You can enter your location on the geomagnetic field calculator by either entering your zip code if you live in the U.S.A or you can select your country and then city from the list. You can also just enter your longitude and latitude if you know what they are.

A degree is a way to measure position on a circle. There are 360 degrees in a circle. Units of degrees are used both for the entry of the location (latitude and longitude) and for the declination results. Latitude is measured north from the equator (0°) to 90° North at the North Pole and south to 90° South at the South Pole. Longitude is measured east (through Europe) and west (over the Atlantic) from Greenwich, England (0°) with 180° E the same as 180° W in the Pacific. Therefore, 45°N 90°E is in China while 45°N 90°W is in Wisconsin. Magnetic declination is measured positive east and negative west from 0° at the magnetic north. Declination values run from 0°-180° east and 0°-180° west. For more information on magnetic declination, see the geomagnetic information FAQ page.

Minutes are a subdivision of a degree. There are 60 minutes in one degree.

Minutes and seconds are used to enter fractions of a degree. There are 60 seconds in one minute and 3600 seconds in one degree.

There are two available magnetic models, the 2005 World Magnetic Model (WMM 2005) and the 10th International Geomagnetic Reference Field model (IGRF 10). The WMM model is valid from 2005-2010. The IGRF model is valid from 1900-2010.

Elevation is measured as the vertical distance from the mean sea level, where the mean sea level is given by the WGS84 ellipsoid. Valid values for the elevation are -10 km to 2890 km. While elevations beyond this range are accepted, result accuracies decline outside the accepted limits.

The step size is the time difference between the returned results in years. For example, if the start and end date are 2 years apart, a step size of 1 year will return two results. If the start and end dates are the same, the step size will automatically be changed to 0. If the start and end dates are different, the step size cannot be 0.

Clicking on the "Get Data File" button will allow you to download your results in a CSV (Comma Separated Value) file format. The first 7 lines of the file explain the contents and list some of the important parameters used to generate the file such as model used, elevation, and location. The data starts on the 9th line and includes the date, declination, inclination, horizontal intensity, north component, east component, verticle component, and total intensity in that order. The last line of the data is the change per year of the same values. Check the first 7 lines of the file for more details.