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The position of the magnetic dip equator at 100 km and the gradient of position with time and altitude are tabulated using the POGO (10/68), GSFC (12/66), and IGRF (10/68) geomagnetic field models. The positions agree within a few tenths of a degree with each other but differ up to 2° from older models and charts. The maximum gradients with time (0.2°/yr) and altitude (−0.3°/100 km) occur to the west of Africa.
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Joseph C. Cain (1969) studied this question.
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