Surya Siddhanta of Varaha as given in his Panca 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 constant as introduced by Varaha by following Brahmagupta's teaching in his Brahmasphuta Siddhanta and the Uttara Khandakhadyaka,
Surya Siddhanta is the most important of this class of works and some attempt should yet be made to ascertain its true date. From internal evidence alone Burgess came to the conclusion that the superior limit to its date is 490A.D. and that the lower limit is 1091 A.D.