that adopted this calendar did so on varying dates. However, all Eastern Orthodox churches continue to use the Julian calendar to determine the date of Easter (except for the Finnish Orthodox Church and the Estonian Orthodox Church, which now use the Gregorian Easter). Arithmetic The following are Gregorian minus Revised Julian date differences, calculated for the beginning of January and March in each century year, which is where differences arise or disappear, until AD 10000. These are exact arithmetic calculations, not depending on any astronomy. A negative difference means that the proleptic Revised Julian calendar was behind the proleptic Gregorian calendar. The Revised Julian calendar is the same as the Gregorian calendar from 1 March 1600 to 28 February 2800, but the following day would be 1 March 2800 (RJ) or 29 February 2800 (G); this difference is denoted as '+1' in the table. 2900 is a leap year in Revised Julian, but not Gregorian: 29 February 2900 (RJ) is the same as 28 February 2900 (G) and the next day will be 1 March 2900 in both calendars - hence the '0' notation. In 900 Julian years there are = 225 leap days. The Revised Julian leap rule omits seven of nine century leap years, leaving leap days per 900-year cycle. Thus the calendar mean year is 365 + days, but this is actually a double-cycle that reduces to 365 + = 365.24 days, or exactly 365 days 5 hours 48 minutes 48 seconds, which is exactly 24 seconds shorter than the Gregorian mean year of 365.2425 days, so in the long term on average the Revised Julian calendar pulls ahead of the Gregorian calendar by one day in 3600 years. The number of days per Revised Julian cycle = 900 × 365 + 218 = 328,718 days. Taking mod 7 leaves a remainder of 5, so like the Julian calendar, but unlike the Gregorian calendar, the Revised Julian calendar cycle does not contain a whole number of weeks. Therefore, a full repetition of the Revised Julian leap cycle with respect to the seven-day weekly cycle is seven times the cycle length = 7 × 900 = 6300 years. Epoch The epoch of the original Julian calendar was on the Saturday before the Monday that was the epoch of the Gregorian calendar. In other words, Gregorian = Julian . However, the Revised Julian reform not only changed the leap