English: Absolute magnitude of the axial dipole component of Earth's magnetic field from 1600 to 2020, according to three models: CALS3k.4, gufm1, and IGRF-12.
Wayback Machine M. Korte and C. Constable (2011). "Improving geomagnetic field reconstructions for 0-3ka". Phys. Earth Planet. Int.188: 247-259.
DOI:10.1016/j.pepi.2011.06.017.
Wayback Machine A. Jackson, A. R. T. Jonkers, and M. R. Walker (2000). "Four centuries of geomagnetic secular variation from historical records". Phil. Trans. R. Soc. Lond. A358: 957-990.
DOI:10.1098/rsta.2000.0569.
IGRF-12: http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html E. Thébault et al. (2015). "International Geomagnetic Reference Field: the 12th generation". Earth, Planets and Space67: 79.