Lunar calendar traces of its origin in the earlier lunar calendar, which continued to be used alongside it for religious and agricultural purposes. Present-day lunisolar calendars include the Chinese, Hindu, and Thai calendars. Synodic months are 29 or 30 days in length, making a lunar year of 12 months about 11 days shorter than a solar year. Some lunar calendars do not use intercalation, such as most Islamic calendars. For those that do, such as the Hebrew calendar, the most common form of intercalation is to add an additional month every second or third year. Some lunisolar calendars are also calibrated by
Vṛṣabha the Tamil Hindu calendar. The ancient and medieval era Sanskrit texts of India vary in their calculations about the duration of Vrsabha, just like they do with other months. For example, the "Surya Siddhanta" calculates the duration of Vrishabha to be 31 days, 10 hours, 5 minutes and 12 seconds. In contrast, the "Arya Siddhanta" calculates the duration of Vrsabha to be 31 days, 9 hours, 37 minutes and 36 seconds. The Indian solar month names are significant in epigraphical studies of South Asia. For example, "Vrsabha" month, along with other solar months, are found inscribed in medieval era Hindu