Resolution No.18 (1973): IGRF1965 and 1975

IAGA, considering that a need exists for a geomagnetic reference field satisfying at least some of several diverse requirements, recommends that the International Geomagnetic Reference Field 1965.0 (IGRF 1965.0) be retained as a standard until 1975.0 after which time it will be replaced by IGRF 1975.0. It is requested that all pertinent observational data be deposited in World Data Centers by 1 January 1975.