Recently the Beast Pieces blog had a post about a 200 year perpetual calendar they printed letterpress. How does a 200 year perpetual calendar work?, I wondered. Unfortunately, the instructions at the bottom are in German, as is the information on the design firm’s website. But then I found this spreadsheet that shows there really are only 14 unique yearly calendars between 1900 and 2099, and then goes on to map each of those 200 years to one of the 14 unique calendars. This begins to help me understand how the German calendar works. Then I found a 10,000 year perpetual calendar with a nifty chart that lets you generate any calendar, without a computer. They both come from calendarhome.com, devoted to all things calendar.
The text underneath the calendar says that to find out which day of the week is on a specific date, you first choose the year you are in which you are in and search in the first table on the top for an attached letter.
Then you choose from the second table (lower left) the month you are currently in and look up a number that stands above the letter you just chose.
Then on the table on the lower right you choose which date you have, look above the number you just figured out, and it tells you what day of the week it is.