Dictionary:International Gravity Formula

Theoretical gravity (as of 1987) is

$978032.68\left({\frac {1+0.00193185138639\sin ^{2}(\phi )}{\sqrt {1-0.00669437999013\sin ^{2}(\phi )}}}\right)\,\mathrm {mGal}$

where is the latitude. Older versions of the IGF are:

$1930:\qquad 978049.0\left(1+0.0052884\sin ^{2}(\phi )-0.0000059\sin ^{2}(2\phi )\right)\,\mathrm {mGal}$

$1967:\qquad 978031.8\left(1+0.0053024\sin ^{2}(\phi )-0.0000058\sin ^{2}(2\phi )\right)\,\mathrm {mGal}$

See latitude correction.