Tuesday's List: Making a Mental Perpetual Calendar

We have always been cursed with a highly irregular calendar system, in spite of the French Revolution's attempted revision to make days of the week resonate with dates of the month...  Many years ago I devised my own mental perpetual calendar to solve this problem: I published it in my February 25, 2009 article: [link].  My system requires adding three different numbers and taking their remainder after dividing by seven to find the day of the week on which any particular date lies...

Here are my assigned numbers:

****BY DAY OF THE WEEK****
Sunday: 0
Monday: 1
Tuesday: 2
Wednesday: 3
Thursday: 4
Friday: 5
Saturday: 6

****BY YEAR****
1956,1984,2012...3 (leap years)
1957,1985,2013...4
1958,1986,2014...5
1959,1987,2015...6
1960,1988,2016...1 (leap years)
1961,1989,2017...2
1962,1990,2018...3
1963,1991,2019...4
1964,1992,2020...6 (leap years)
1965,1993,2021...0
1966,1994,2022...1
1967,1995,2023...2
1968,1996,2024...4 (leap years)
1969,1997,2025...5
1970,1998,2026...6
1971,1999,2027...0
1972,2000,2028...2 (leap years)
1973,2001,2029...3
1974,2002,2030...4
1975,2003,2031...5
1976,2004,2032...0 (leap years)
1977,2005,2033...1
1978,2006,2034...2
1979,2007,2035...3
1980,2008,2036...5 (leap years)
1981,2009,2037...6
1982,2010,2038...0
1983,2011,2039...1

***BY MONTH***
Jan (leap year):3
Jan (non-leap):4
Feb (leap year):6
Feb (non-leap):0
March: 0
April: 3
May: 5
June: 1
July: 3
August: 6
September: 2
October: 4
November: 0
December : 2

Once you memorize the above...the days of the week are easy, the years follow a 28-year cycle and have a pattern to their number...only the months' numbers may seem arbitrary. You add the assigned number of the month, the numerical date, and the assigned number of the year all together, divide by seven and take the remainder to find the day of the week.  I suggest that at the start you just memorize the numbers of a few years around 2017...say, 2015-2020...

Some examples:

a) July 11, 2017 (today's date)
       3  +  11  +   2=  16...dividing by 7 yields a remainder of 2, so it's Tuesday.

b) November 22, 1963 (the day Kennedy was assassinated):
       0  +  22  +  4 =  26....dividing by 7 yields a remainder of 5, so it was on a Friday.

c) July  4, 1976 (Bicentennial Day)
      3    +  4    +  0 =  7....dividing by 7 yields a remainder of 0, so it was on a Sunday.

d) December 25, 2017
      2  +  25  +  2 = 29....dividing by 7 yields a remainder of 1, so Christmas this year falls on Monday.

I admit it: memorizing the numbers may seem a little challenging, but you can also take it year-by-year and just remember that this year, 2017, is "2" and then you only have to know by rote the months and be able to divide mentally by 7.  That still may be a bit too much for many, and besides, nowadays folks can usually just look at their smartphones.  But it was still a fun little project of mine, and the more you work at it, the easier and quicker this system is to use.  And if you're stuck in a long line somewhere, you can practice this instead of automatically checking your messages and Facebook...