Resolution No.21 (1971): Vector field measurement at repeat stations

The IAGA recognising the shortage and poor distribution of present ground level data for evaluating geomagnetic secular change, urges all countries to measure the vector field at their repeat stations at least once in 10 years, more frequently in regions with special features (e.g. secular variation foci, tectonically anomalous areas, etc.) and, where appropriate, to set up repeat stations on the islands of the South Pacific and Atlantic Oceans and to report results promptly to World Data Centers or organisations that prepare world charts.