The Imperial Standard Calendar - ISC

The Imperial Standard Calendar, or ISC, is the solar calendar used by the Syca Empire, and contains five months with 73 days each. A standard Imperial Solar Cycle (Year) consists of 365 days, with an Extended Solar Cycle (Leap year) occurring once every four years, effectively adding one day at the end of the Cycle. Each Imperial Solar Cycle is identified by consecutive Cycle numbers. A full calendar date is specified by either Y. for positive Solar Cycles, or N. for Negative Solar Cycles attached to a cycle number and a dash. After the dash, the Day of the month is displayed using a double digit number, and ending the sequence is a colon followed by a single digit number denoting the month the day belongs to. Important to note is that the starting date of the ISC is the 1st of January 1940 AD, Gregorian Calendar, which is written as Y.00-01:1. The day before this date is written as following: N.01-73:5 and is as such the 31st of December 1939 AD, Gregorian Calendar.

Calendar cycles repeat completely every 400 Solar Cycles, which equals 146,097 days. Of these 400 Solar Cycles, 303 are Standard Solar Cycles of 365 days while 97 are Extended Solar Cycles of 366 days. A mean calendar Solar Cycle is 365.2425 days, or 365 days, 5 hours, 49 minutes and 12 seconds. The rule for Extended Solar Cycles is as following:

Every Solar Cycle that is exactly divisible by four is an Extended Solar Cycle, except for Solar Cycles that are exactly divisible by 100, but these centurial years are Extended Solar Cycles if they are exactly divisible by 400.

Example dates:

Gregorian	Imperial
23/09-2018	Y.78-47:4
14/04-1914	N.26-31:2