Perpetual Calendar
A perpetual calendar is a calendar valid for many years, usually designed to look up the day of the week for a given date in the past or future. For the Gregorian and Julian calendars, a perpetual calendar typically consists of one of three general variations: # 14 one-year calendars, plus a table to show which one-year calendar is to be used for any given year. These one-year calendars divide evenly into two sets of seven calendars: seven for each common year (the year that does not have a February 29) with each of the seven starting on a different day of the week, and seven for each leap year, again with each one starting on a different day of the week, totaling fourteen. (See Dominical letter for one common naming scheme for the 14 calendars.) # Seven (31-day) one-month calendars (or seven each of 28–31 day month lengths, for a total of 28) and one or more tables to show which calendar is used for any given month. Some perpetual calendars' tables slide against each othe ...
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Determination Of The Day Of The Week
The determination of the day of the week for any date may be performed with a variety of algorithms. In addition, perpetual calendars require no calculation by the user, and are essentially lookup tables. A typical application is to calculate the day of the week on which someone was born or a specific event occurred. Concepts In numerical calculation, the days of the week are represented as weekday numbers. If Monday is the first day of the week, the days may be coded 1 to 7, for Monday through Sunday, as is practiced in ISO 8601. The day designated with 7 may also be counted as ''0'', by applying the arithmetic modulo 7, which calculates the remainder of a number after division by 7. Thus, the number 7 is treated as 0, 8 as 1, 9 as 2, 18 as 4 and so on. If Sunday is counted as day 1, then 7 days later (i.e. day 8) is also a Sunday, and day 18 is the same as day 4, which is a Wednesday since this falls three days after Sunday. The basic approach of nearly all of the methods to ...
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Cheque
A cheque, or check (American English; see spelling differences) is a document that orders a bank (or credit union) to pay a specific amount of money from a person's account to the person in whose name the cheque has been issued. The person writing the cheque, known as the ''drawer'', has a transaction banking account (often called a current, cheque, chequing, checking, or share draft account) where the money is held. The drawer writes various details including the monetary amount, date, and a payee on the cheque, and signs it, ordering their bank, known as the ''drawee'', to pay the amount of money stated to the payee. Although forms of cheques have been in use since ancient times and at least since the 9th century, they became a highly popular non-cash method for making payments during the 20th century and usage of cheques peaked. By the second half of the 20th century, as cheque processing became automated, billions of cheques were issued annually; these volumes peaked ...
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Long Now Foundation
The Long Now Foundation, established in 1996, is an American non-profit organization based in San Francisco that seeks to start and promote a long-term cultural institution. It aims to provide a counterpoint to what it views as today's "faster/cheaper" mindset and to promote "slower/better" thinking. The Long Now Foundation hopes to "creatively foster responsibility" in the framework of the next 10,000 years. In a manner somewhat similar to the Holocene calendar, the foundation uses 5-digit dates to address the Year 10,000 problem (e.g., by writing the current year "0" rather than ""). The organisation's logo is , a capital X with an overline, a representation of 10,000 in Roman numerals. Projects The foundation has several ongoing projects, including a 10,000-year clock known as the ''Clock of the Long Now'', the ''Rosetta Project'', the ''Long Bet Project'', the open source ''Timeline Tool'' (also known as Longviewer), the ''Long Server'' and a monthly seminar series. Clo ...
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Doomsday Rule
The Doomsday rule, Doomsday algorithm or Doomsday method is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years. The algorithm for mental calculation was devised by John Conway in 1973, drawing inspiration from Lewis Carroll's perpetual calendar algorithm. It takes advantage of each year having a certain day of the week upon which certain easy-to-remember dates, called the ''doomsdays'', fall; for example, the last day of February, 4/4, 6/6, 8/8, 10/10, and 12/12 all occur on the same day of the week in any year. Applying the Doomsday algorithm involves three steps: Determination of the anchor day for the century, calculation of the anchor day for the year from the one for the century, and selection of the closest date out of those that always fall on the doomsday, e.g., 4/4 and 6/6, and count of the number of days ( modulo 7) between that date and the date in question ...
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Permanent Calendar Gregorian
Permanent may refer to: Art and entertainment * ''Permanent'' (film), a 2017 American film * ''Permanent'' (Joy Division album) * "Permanent" (song), by David Cook Other uses *Permanent (mathematics), a concept in linear algebra *Permanent (cycling event) *Permanent wave, a hairstyling process See also *Permanence (other) *''Permanently'', a 2000 album by Mark Wills *Endless (other) *Eternal (other) *Forever (other) *Impermanence Impermanence, also known as the philosophical problem of change, is a philosophical concept addressed in a variety of religions and philosophies. In Eastern philosophy it is notable for its role in the Buddhist three marks of existence. It is ...

Zeller's Congruence
Zeller's congruence is an algorithm devised by Christian Zeller in the 19th century to calculate the day of the week for any Julian calendar, Julian or Gregorian calendar date. It can be considered to be based on the conversion between Julian day and the calendar date. Formula For the Gregorian calendar, Zeller's congruence is :h = \left(q + \left\lfloor\frac\right\rfloor + K + \left\lfloor\frac\right\rfloor + \left\lfloor\frac\right\rfloor - 2J\right) \bmod 7, for the Julian calendar it is :h = \left(q + \left\lfloor\frac\right\rfloor + K + \left\lfloor\frac\right\rfloor + 5 - J\right) \bmod 7, where * ''h'' is the day of the week (0 = Saturday, 1 = Sunday, 2 = Monday, ..., 6 = Friday) * ''q'' is the day of the month * ''m'' is the month (3 = March, 4 = April, 5 = May, ..., 14 = February) * ''K'' the year of the century (year \bmod 100). * ''J'' is the zero-based numbering, zero-based century (actually \lfloor year/100 \rfloor) For example, the zero-based centuries for 1995 a ...
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Perennial Calendar
A perennial calendar is a calendar that applies to any year, keeping the same Calendar date, dates, weekdays and other features. Perennial calendar systems differ from most widely used calendars which are annual calendars. Annual calendars include features particular to the year represented, and expire at the year's end. A perennial calendar differs also from a perpetual calendar, which is a tool or reference to compute the weekdays of dates for any given year, or for representing a wide range of annual calendars. For example, most representations of the Gregorian calendar year include weekdays and are therefore annual calendars, because the weekdays of its dates vary from year to year. 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. History and background The term ''perennial calendar'' appeared as early as 1824, in the title of Thomas Ignatius Maria Forster's ''Pere ...
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