arrangement is known as maximal evenness. The 52/293 leap cycle has a calendar mean year of 365+71/293 days, or 365 days 5 hours 48 minutes and about 56.5 seconds, which is intentionally slightly shorter than the present era mean northward equinoctial year of 365 days 5 hours 49 minutes and 0 seconds (mean solar time). Calendar arithmetic The Kalendis calendar calculator demonstrates the Symmetry454 calendar and interconverts dates between Symmetry454 and a variety of other calendars. The Symmetry454 arithmetic is fully documented and placed in the public domain for royalty-free computer implementation. Officially, Symmetry454 has been running since January 1, 2005, which was the first New Year Day after it came into existence. Its proleptic epoch, however, was on the same day as the proleptic epoch of the Gregorian Calendar = January 1, 1 AD. Easter on a fixed date Tentatively, Sunday April 7 on the Symmetry454 Calendar is proposed as a fixed date for Easter, based on a frequency analysis of the distribution of the Gregorian or Astronomical Easter dates. There are only five possible dates for Easter within the Symmetry454 Calendar, since only day numbers divisible by 7 can be a Sunday. The three highest-frequency dates upon which Easter can land are March 28, April 7, and April 14. Selecting the middle date (April 7) would fix Easter at its median position within its distribution range. See also 4–4–5 calendar: Similar month structure. References "Designs for a new year", in the "Innovators" section of the Toronto Star newspaper, Friday, December 24, 2004, page A3, by reporter Peter Gorrie. "Star Trek Math Inspires Calendar Reform", Discovery Channel, Thursday, December 30, 2004, by Jennifer Viegas, Discovery News. "Time and Again, the Calendar Comes Up Short: Sticklers for Symmetry Lament Imperfections in the 400-Year-Old Gregorian System; Earth's Inconvenient Orbit", The Wall Street Journal, December 31, 2009, by Charles Forelle, The Numbers Guy. "New Year’s Revolution: A proposed new calendar would give February an extra week and start every month on a Monday", University of Toronto Magazine, in Leading Edge, Winter 2011, by Scott Anderson. External links The Symmetry454 Calendar (full specifications, FAQs, arithmetic) The Kalendis Calendar Calculator (freeware) The Lengths of the Seasons (numerical integration analysis) Solar Calendar Leap Rule Studies (shows why the 52/293 leap rule is preferred) Proposed calendars Leap week calendars Specific calendars 2005 introductions