The flattening value varies slightly from one reference ellipsoid to another, reflecting local conditions and whether the reference ellipsoid is intended to model the entire Earth or only some portion of it.

Then they are able to correct the height above WGS ellipsoid to the height above WGS84 geoid.

)The difference between a sphere and a reference ellipsoid for Earth is small, only about one part in 300.

In the early 19th century, the flattening of the earth ellipsoid was determined to be of the order of 1 300 (Delambre, Everest).

The curve produced by the angular velocity vector on the inertia ellipsoid, is known as the polhode, coined from Greek meaning path of the pole .

To determine the equation of the stress ellipsoid we consider the coordinate axes formula_1 taken in the directions of the principal axes, i.e., in a principal stress space.

This hydrostatic model of the shape of the Earth was founded on a paper by Colin Maclaurin, which had shown that a mass of homogeneous fluid set in rotation about a line through its centre of mass would, under the mutual attraction of its particles, take the form of an ellipsoid.