Only perpetual calendars meet the basic condition to permit the deduction of any essential data from any other data (year, month, week and day). However, all the analog perpetual calendars known are hardly perpetual since the limit of their calculations is about 50 years.
Our calendar starts at January 1, 1600, and ends at December 31, 2799. It is based on a repeating cycle of 400 years and a solar cycle of 28 years. It works by means of the "Dominical letter".