U.S. world chart model coefficients for 1975



The 1975 U.S. World Magnetic Chart Model (AWC/75| will be the basis for the 1975 edition of the World Magnetic Chart series to be published by the U.S. Naval Oceanographic Office.

The model consists of a degree 12 spherical harmonic series of 168 internal main-field coefficients and a degree 8 series of 80 secular change coefficients. The coefficients, presented in the accompanying table, are of the Schmidt quasi-normalized type and are to be used with a reference sphere of radius 6371.2 km.