Comparison: Chinese Calendar vs. Western Calendar
As early as in the Shang Dynasty (16th-11th century BC), when China was already a farming country, the ancient people used the concept of leap month to decide the four seasons, and by the Warring States Period (475-221BC), the measured length of a solar year was quite precise. In the Western countries, however, the calendar was still in a mess by the time of China's Western Han Dynasty (206BC-24AD).
Ancient Chinese people learned of the "seven leap months in 19 years" 200 years earlier than the Greeks.
Whenever the Western countries carried out a calendar reform, they preferred to improve the coordination between the year, month, and day, leaving other parts unchanged. In ancient China, however, a calendar reform usually involved inferring the astronomic constants and the problem of solar and lunar eclipses as well as the planets' movement.
The astronomic development was highly emphasized in ancient China in terms of the calendar, contributing a lot to the development of calendars in other countries.