Elliptical constant

[Epsilon=One]

There is a constant that applies to an ellipse of any shape such that when a structural part is set to this constant, every other structural part (perigee, focal length, diameters, chords, apogee, etc.) has the same geometric ratio to one another within any ellipse.

An ellipse so defined has relevance to subatomic structure.

What is the value of the constant?