Thanks to Dr T.S. Kelso for making available his Turbo Pascal code of NORAD SGP4/SDP4 orbital models which I referenced to create code in SkyTrack.
In addition, thanks
to Dr Kelso for permitting direct links to his website at https://celestrak.com for the downloading of TLE files.
Various calculations were used from
Astronomical Algorithms Second Edition 1998 by Jean Meeus
Thanks to those who assisted with beta-testing of SkyTrack.
Thanks to John Eccles for maintaining and supporting Satellite Tracker from 2013-2019.