I reckon it isn't that inaccurate, especially given the reported behaviour of compasses. "From these models and extrapolating down into the Earth, it is known

I reckon it isn't that inaccurate, especially given the reported behaviour of compasses. "From these models and extrapolating down into the Earth, it is known that regions of reversed flux at the core-mantle boundary have grown over time. In these regions the compass points in the opposite direction, in or out of the core, compared to that of surrounding areas. It is the growth in area of such a reversed flux patch under the south Atlantic that is primarily responsible for the decay in the main dipolar field. This reverse patch is also responsible for the minimum in field strength called the South Atlantic Anomaly, now centred over south America. In this region energetic particles can approach Earth more closely, causing increased radiation risk to low Earth orbit satellites." http://www.geomag.bgs.ac.uk/education/reversals.html http://www.geomag.bgs.ac.uk/education/reversals.html