Abstract
A spheroid approximates the earth more accurately than does a sphere. Before analyzing the data over the surface of the earth by spherical harmonic series, we must correct them to the appropriate values on a true sphere. The change in the earth's radius and latitude, and in the direction of the vector components must be considered. The corrections have been applied here to values derived from existing analyses of the earth's magnetic field. The changes are significant, the largest being about 120γ in the g30 term.
