geomag-wmm

WMM library used to calculate the magnetic declination.

You must download the WMM.COF file corresponding to the model you want to use, for instance, 2020-2025.

The code passes the 12 cases presented in the WMM description, Section 1.11 Table 6.

There is no guarantee that it is correct. It does not calculate the grid variation (yet) and does not warn the user if they calculate in a low precision area.