This is fairly interesting:
Quote:
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Irregular changes in the Earth’s core field limit the lifetime of any predictive model such as the WMM. For this reason a revision (WMM2015) was released in December 2014, valid until 2020. In September 2018 version 2 of WMM2015 (WMM2015v2 valid 2015.0-2020.0) was released after feedback from users to the announcement in March 2018 that WMM2015 had become inaccurate in the Arctic region and was not meeting its accuracy requirements. These models were produced by BGS jointly with the US National Centres for Environmental Data (NCEI), with funding from the Defence Geographic Centre in the UK and the US National Geospatial-Intelligence Agency.
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World Magnetic Model (WMM)
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"There are more instances of the abridgment of freedom of the people by gradual and silent encroachments of those in power than by violent and sudden usurpations"
James Madison
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