Q. Which is India's oldest calendar?

Hindu Calendar is the oldest calendar in India. Subhash Kak claims that the first day of the Hindu calendar occurred considerably earlier in time. He uses Greek historians' descriptions of Maurya kings to highlight the calendar's 6676 BCE inception date (it's called the Saptarsi calendar). King Vikramaditya is honored with the beginning of the Vikrami calendar in 57 BCE.