Formula used to determine the gravitational acceleration at a given latitude (gφ) for a model of the Earth that comprises a rotating, oblate spheroid. gφ= g0(1 + α sin2 φ + β sin2 φ), where g0 is the value at the equator, of 978.0318 gals, φ is the latitude, and the constants α and β are 0.0053024 and −0.0000058.