For this reason, proposals to perennialize the Gregorian calendar typically introduce one or another scheme for fixing its dates on the same weekdays every year.
[1] In that work he compiled "the events of every day in the year, as connected with history, chronology, botany, natural history, astronomy, popular customs and antiquities, with useful rules of health, observations on the weather, explanations of the feasts and festivals of the church and other miscellaneous useful information".
Often printed in perennial-calendar format also are book blanks for diaries, ledgers and logs, for use in any year.
Entries on the blank pages of these books are organized by calendar dates, without reference to weekdays or year numbers.
Two methods favored for perennializing the calendar are the introduction of so-called "blank days" and of a periodic "leap week".
In the twelve-month plan of The World Calendar, for example, the Gregorian year-end date of December 31 is sequestered from the cycle of the week and celebrated as "Worldsday".
The Christian celebration of Easter is historically calculated to occur on the first Sunday after the first ecclesiastical full moon falling on or after 21 March.
[6] The Symmetry454 calendar proposes Sunday, April 7 as a permanently fixed date for Easter, based on the median date of the Sunday after the day of the astronomical lunar opposition that is on or after the day of the astronomical northward equinox, calculated for the meridian of Jerusalem.
[7] In 1963 the Second Ecumenical Council of the Vatican declared: "[The Vatican] would not object if the feast of Easter were assigned to a particular Sunday of the Gregorian Calendar... [and] does not oppose efforts designed to introduce a perpetual calendar into civil society.
Another option would trim every year to exactly 364 days, allowing the calendar months to drift relative to the seasons.