Jōkyō calendar

The Jōkyō calendar (貞享暦) was a Japanese lunisolar calendar, in use from 1684 to 1753. It was officially adopted in 1685.

History
The Jōkyō-reki system was developed and explained by Shibukawa Shunkai. He recognized that the length of the solar year is 365.2417 days.

Shibukawa discovered errors in the traditional Chinese calendar, the Senmyō calendar, which had been in use for 800 years.