In order to develop the software, I had to research on a lot of books. They are
Celestial Mechanics by Laplace
Astronomia Nova – Kepler
Bryon’s Astronomy
the Encyclopaedia Brittanica Astronomical tables by Newcombe
and Indian Books
Siddhanta Sekhara by Sripathi
Ganitha Nirnayam by Puliyur
To study Astronomy was difficult and later to implement the formulae was also difficult. But then I persevered and developed the Vedic Astrology software