Jōkyō calendar

The Jōkyō calendar (貞享暦, Jōkyō-reki) was a Japanese lunisolar calendar, in use from 1684 to 1753.

[1] It was officially adopted in 1685.

[2] The Jōkyō-reki system was developed and explained by Shibukawa Shunkai.

[3] He recognized that the length of the solar year is 365.2417 days.

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