There are two modules in this distribution. Date::Doomsday calculates doomsday for a particular year. Date::DayOfWeek uses the doomsday algorithm to calculate the day of the week for any given date. Doomsday is a cute little idea invented by Dr John Conway that makes it very easy to figure out the day of the week for any date. For more information about the origins and mathematics surrounding doomsday, see the following web sites: http://rudy.ca/doomsday.html http://quasar.as.utexas.edu/BillInfo/doomsday.html http://www.cst.cmich.edu/users/graha1sw/Pub/Doomsday/Doomsday.html WWW: https://metacpan.org/release/Date-DayOfWeek