Use Calculate U.S. Historic
Declination under the U.S. Historic Declination tab of the Magnetic Field Calculators page,
then click Calculate at the bottom. See below for form section explanations.
If you do not know the longitude and latitude, use Lookup Latitude / Longitude in the box to the right of the calculator,
which will populate the longitude and latitude values in the calculator form for you.
If Lookup Latitude / Longitude can't find your location, search for an address at USGS Earth Explorer.
For degrees, minutes, and seconds, separate the values with a space (there are 60 seconds in a minute and
60 minutes in a degree, therefore 35° 30' 0" is equivalent to 35.500). Do not enter the N or W
designation. The value should be positive and the hemisphere should be designated by
selecting a value from the choices to the right of the text field. N stands for northern hemisphere
latitude, and W for western hemisphere longitude. The USA is (mostly) located in the northern (N) and
western (W) hemispheres, and have been pre-selected. Latitude ranges are limited from 25°
North to 52° North, and longitude ranges are limited from 130° West to 65° West.
An XML document with U.S. Historic magnetic field values in Boulder for 2000 through 2010: