Dating service for buddhists
One key difference with Indian systems is that the Burmese system has followed a variation of the Metonic cycle.It is unclear from where, when or how the Metonic system was introduced; hypotheses range from China to Europe.This means reading ancient texts and inscriptions in Thailand requires constant vigilance, not just in making sure one is correctly operating for the correct region, but also for variations within regions itself when incursions cause a variation in practice.
This provides 20819 complete days to both calendars.
This 57-year cycle would provide a mean year of about 365.2456 days and a mean month of about 29.530496 days, if not corrected.
As such, the calendar adds an intercalary month in leap years and sometimes also an intercalary day in great leap years.
The calculation methodology of the current versions of Southeast Asian Buddhist calendars is largely based on that of the Burmese calendar, which was in use in various Southeast Asian kingdoms down to the 19th century under the names of Chula Sakarat and Jolak Sakaraj.
The Burmese calendar in turn was based on the "original" Surya Siddhanta system of ancient India (believed to be Ardharatrika school).