Oblate spheroid equation help In the section < Could someone tell me what $e$ and $f$ are in this first formula? $$ \beta(\phi) = \tan^{-1}\left(\sqrt{1-e^2}\tan\phi\right) =\tan^{-1}\left((1-f)\tan\phi\right) $$ Also, is $\tan^{-1}$ the same as $\arctan$? (Sorry, I am more used to typing formulas into programming source code, not using pen and paper.) Thanks.

$e$ is the eccentricity) of the polar cross-section. $f$ is its oblateness, or (first) flattening. And yes, $\tan^{-1}$ is the same as arctan.