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The Human Calendar (4 centuries)

Instructions Example:
November 12, 2070
Step 1: Determine the code for the century:

Century: 1800's 1900's 2000's 2100's
Code # 2 0 6 4
Century = 2000's
The code for 2000's is 6

Shortcut: Use -1 instead of 6 for 2000's to make the arithmetic easier.

Total = 6

Flashcards
Step 2: Determine the code for the year:

Year: 00 04 08 12 16 20 24
28 32 36 40 44 48 52
56 60 64 68 72 76 80
84 88 92 96  
Code #1642053
Year = 70

68 is 2, so 69 is 3 and 70 is 4!

Total = 10 (6 + 4)

Flashcards
Step 3: Determine month code:

Jan = 6
Feb = 2
Mar = 2
Apr = 5
May = 0
Jun = 3
Jul = 5
Aug = 1
Sep = 4
Oct = 6
Nov = 2
Dec = 4
Month = November

November = 2

Total = 12 (6 + 4 + 2)

Flashcards
Step 4: Determine date code:

Date:   1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31  
Code #0123456
Date = 12

The code for date:12 is 5.

Total = 17(6 + 4 + 2 + 5)

Shortcut #1: Subtract 7, 14, 21 or 28, from the date to find code, dates less than 7 are already equal to the code.
Example:
Nov 12: 12 - 7 = 5.
Example:
Nov 26: 26 - 21 = 5

Shortcut #2: Simply add the date to the total. Example: Nov 12: Code=12, Total = 24 (6 + 4 + 2 + 12).

Flashcards
Step 5: Determine day-of-week from total

Divide the total from Step 3 by seven, the remainder giving the day-of-week:

Day-of-week: Sun Mon Tue Wed Thu Fri Sat
Remainder:0123456
Total = 17 (Century=6, Year=4, Month=2, Date=5)

17 divided by 7 is:
2 remainder 3

3 = Wednesday

Shortcut: Instead of dividing, just subtract 7, 14, 21, 28, or 35, etc. (multiples of 7) until you have a number 0 to 6. For example, 17 - 14 = 3. If the total was 30, then 30 - 28 = 2 = Tuesday.

Flashcards
More Flashcards
Step 6: Don't forget leap-year!

Subtract 1 at any point in the process only if the year is a leap year, and the month is January or February!
2070 is not a leap year.

Shortcut #1: The year is a leap year if it is found in the table in step 1. (68 and 72 are leap years, but 70 is not)

Shortcut #2: A year is a leap year if it is evenly divisible by 4.

Shortcut #3: As a last step, you can simply take the day before (if the year is a leap year, and the month is Jan. or Feb.)

Click here for the rare exceptions to the above shortcuts.
Flashcards



Click here for flashcards for 1800 to 2199.


Tips and Tricks

 Some may find it easier to combine the century and year code first, then combine the month and date code, and then add the 2 numbers together for a final total, and proceed to step 5 from there.

 Click here for a printable one-page quick reference.

 Please let us know your success stories if you master this system!


Links

 Calendar Memory Records

 Doomsday Algorithm - Gaudy yet informative site showing a different approach to the human calendar, originally created by mathematician-great John Horton Conway