What is the connection between Tibetan calendar and Han calendar?

The traditional calendar of Tibetans in China, according to historical records, Tibetans had their own calendar before 100 BC, and the days, months and years were calculated according to the full moon and short month. In the 7th century, Princess Wencheng and Princess Jincheng of the Tang Dynasty successively entered Tibet, bringing with them the calendar of the Tang Dynasty. Since then, the Tibetan ancient calendar has been combined with the Han calendar and Indian calendar, forming a unique five-element calendar in heavenly stems and earthly branches in the Yuan Dynasty.