Like ArchKalmag, HistKalmag is a correlation-based model of the geomagnetic core field, which covers the historical period. Measurements of the magnetic field direction, in particular the declination, are available for the last 400 years. These values were mainly measured by ships for navigation purposes and documented in logbooks. However, a method for absolute measurement of field intensity was not developed until 1830 by Carl-Friedrich Gauss, so there are no older measurements of field strength. For the HistKalmag model, historical observations and archaeomagnetic data were therefore combined so that the model covers the magnetic field development of the last 1000 years.

Reference:

Schanner, M., L. Bohsung, C. Fischer, M. Korte and M. Holschneider (2023): The global geomagnetic field over the historical era: what can we learn from ship-log declinations? Earth Planets Space, 75, 96. doi.org/10.1186/s40623-023-01852-1

The model is available from this website: https://ionocovar.agnld.uni-potsdam.de/Kalmag/Histo/