There is also this useful site that lets you pick your loction on a map and tells you the magnetic declination. The ruler tool in Google Earth shows ‘heading’, so once you know your magnetic ...

To correct magnetic declination, you’ll need to know the declination information for your area. Usually, you’ll be able to find this on topographic maps. That said, if your map is old ...

the exact nature of this 'map' has been the subject of ongoing debate. In a carefully designed experiment, warblers were exposed to artificially altered magnetic inclination and declination values ...

This map shows the location of the north magnetic pole (the white star) and the magnetic declination (see contour interval of 2 degrees) at the beginning of 2019. Courtesy of NOAA NCEI/CIRES ...