The compression factor is b/a in each case. For the ellipse, this factor is also the aspect ratio of the ellipse. There are two other variants of flattening (see below) and when it is necessary to avoid confusion the above flattening is called the first flattening. The following definitions may be found in standard texts and online web texts == De... Found on http://en.wikipedia.org/wiki/Flattening
(from the article `geoid`) An ellipsoid of revolution is specified by two parameters: a semimajor axis (equatorial radius for the Earth) and a semiminor axis (polar radius), or ... Found on http://www.britannica.com/eb/a-z/f/35