Geomagnetic data are held by a number of World Data Centres (WDC) with each Centre having different holdings and different methods of distribution. These Centres are run by institutes in Boulder, Edinburgh, Kyoto, Moscow and Mumbai. Using data from two of these WDCs we describe methods to compare temporal coverage of data, and, importantly, the data themselves. \ud This study examines the hourly data common to Edinburgh and Kyoto and gives details of the number of observatory-years of data where disagreements are found, and quantifies the level of disagreement. We show several examples of datasets that differ between the two WDCs, and report on the nature of the differences in detail. Finally, we explore possible reasons for the differences found between the data holdings and suggest next steps towards the unification of the WDC data holdings.\ud \u
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