A Perpetual Calendar for 2012

During the year, 2012, there may be times when you'll need to know what is the day of the week for various dates. You won't need a calendar to find out when you use the method described in this article.

Those of you who are familiar with the Perpetual Calendar on the front cover of The Lighter Side of Math will recognize that the calendar described here is only of one year from the 400 Year version in that book. The see the larger version, search for Perpetual Calendar Farina with Google and use the site that appears at the top of the listing. The author of this article has been interested in designing perpetual calendars for about sixty years.

To use the 2012 version, you must first memorize a small table entitled Key Values for Months that has twelve entries in it. Or, you can attach the table to the wall of your working space. Here is the table:

Key Values for Months
January = 6
February = 2
March = 3
April = 6
May = 1
June = 4
July = 6
August = 2
September = 5
October = 0
November = 3
December = 5

To find the day of the week for a particular date in 2012, do this:

1. Write down the date, example, June 11.
2. Look up the key value for June in the above table and
remember it. In this example, that value is 4.
3. Add the day of the month to the key value.
In this example, the number to add is 11. The sum is 15.
4. Divide the sum by 7 and remember only the remainder.
In the example, when you divide 15 by 7, the remainder is 1.

With zero representing Sunday, 1 representing Monday, etc.,
the above remainder indicates that June 11, 2012 falls on a Monday.

Another example:

In 2012, on what day of the week does July 4 fall?
The key value for July is 6. Add 4 to 6 and the result is 10.
Divide 10 by 7 and the remainder is 3.
With zero representing Sunday, the remainder 3 represents Wednesday.
Therefore, July 4, 2012 falls on a Wednesday.

To use this scheme mentally, memorize the 12 key values. Employ the method
described above and use the final number to tell you the day of the week. Remember
that zero represents Sunday, 1 represents Monday, 2 represents Tuesday, etc.