I've spent the last several months trying to decipher an 1860 English translation of the #SuryaSiddhanta, which was originally written in #Sanskrit and published in its final form in KY 3606 (505 AD). After tracing multiple errors and bugs, I've finally gotten a pretty accurate algorithm which agrees with the methods of late Classical Indian #astronomy as well as observations...
And it looks like modern Indian Solar New Year is actually synched to the #GregorianCalendar.