A Text Book of Hindu Astronomy, Surya Siddhanta of Varaha as given in his Pancha-siddhantika are almost the same as those of the Khandakhadyaka, it is clear that the old Surya Siddhanta was made up to date by Varaha by replacing the old constants in it by new ones from Aryabhata I's 'midnight' system. A subsequent redactor of the Surya Siddhanta changed the constants as introduced by Varaha by following Brahnagupta's teachings in his Brahmasphuta Siddhanta and the Uttara Khandakhadyaka. Surya Siddhanta is the most important of this class of works & some attempt should yet be made to ascertain its true date. From internal evidence alone Burgees came to the conclusion that the superior limit to its date is 490 A.D. and that the lower limit is 1091 A.D. Similarly between the Brahmasphuta Siddhanta and the modern Surya Siddhanta, we believe that we have established our view as to the nature of the modern Surya Siddhanta.