The Cresian calendar is a nonstandard system of timekeeping on Cresia. The official system of timekeeping is Derived Time (DT), required on all official documents. However, the Cresian calendar and Cresian Time (CT) is used for everyday life. The tropical year of Cresia is 325.872934635 dd, and its solar day 13.506965621 dh. Thus, there are 241.262874127 solar days in a tropical year, or about 9,650,515 days in 40,000 years. Any year that is divisible by 4, 50, or 125 is a leap year, unless it is also divisible by 800 but not 8000, which results in 10,515 leap years per 40,000 years.