is off by one compared to the original month-length component over the required range of , resulting in a starting value of 0 for Sunday. See also Determination of the day of the week Doomsday rule ISO week date Julian day References Bibliography Each of these four similar imaged papers deals firstly with the day of the week and secondly with the date of Easter Sunday, for the Julian and Gregorian calendars. The pages link to translations into English. External links The Calendrical Works of Rektor Chr. Zeller: The Day-of-Week and Easter Formulae by J R Stockton, near London, UK. The site includes images and translations of the above four papers, and of Zeller's reference card "Das Ganze der Kalender-Rechnung". Gregorian calendar Julian calendar Calendar algorithms Modular arithmetic