Fig. 3From: DTU candidate field models for IGRF-12 and the CHAOS-5 geomagnetic field model Top: Locations of the 159 ground magnetic observatories where secular variation estimates were derived using annual differences of revised monthly means. Observatories whose predictions are shown in Fig. 5 are marked in red and labelled. Bottom: the number of observatories with secular variation estimates available per monthBack to article page