Dedicated F.S.
To calculate like a Rain-Man
Since in 2013 an adult was born in 19xx you must add only THREE numbers to get the week day:
To calculate like a Rain-Man
-
the day of the week for an adult’s birthday
-
the day they were born
-
the day they will turning 80
-
what day birthday will be this year
-
and what it would have been 100 years
is a very simple calendar
feat.
Since in 2013 an adult was born in 19xx you must add only THREE numbers to get the week day:
Month key number, day and year key number.
We need to convert weekday,
month and year into key-numbers and subtract multiples of 7.
Week day key numbers:
For Sunday to Saturday: 0 … 6
Month key numbers:
For January to December: 033 614 625 035
In leap years, January and February reduced by one to 6 and 2!
Day:
Simply use the days from 1 to 31.
Year key numbers (you only need the last 2 digits of the year):
For the years 00 – 99 the year codes do change in a pattern that repeats
every 28 years. So you can shorten the year by multiples of 28:
00 – 27 are the
same years as 28 – 55 and so on.
Year:
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34
35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55
56 57 58
59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83
84 85 86 87 88 89 90 91 92 93 94 95
96 97 98 99
Year code:
0 1 2 3 5 6 0 1 3 4 5 6 1 2 3 4 6 0 1 2 4 5 6 0 2 3 4 5
0 1 2 3 5 6 0 1 3 4 5 6 1 2 3 4 6 0 1 2 4 5 6 0 2 3 4 5
For years in 20xx subtract 1.
One should learn this year codes by heart.
Examples:
I. June, 27th
1978
Weekday:
June code is 4; year 78 minus 2*28 is 22, code is 6:
4 (June) + 27 + 6 (year 78) = 37
shorten by multiples of 7 (5*7=35) gives 2
Tuesday.
Turning 80:
Work out which day is always 2 days later:
Tuesday and 2 days later is a Thursday.
This year (year 13 in 20xx; code is 2-1=1)
June, 27th
2013:
4 (June) + 27 + 1 (year 13 in
20xx) = 32 shorten by multiples of 7 (4*7=28) gives 4
Thursday.
100 years later:
Work out which day is always 1 day before:
Tuesday and 1 days before is a Monday.
II. January, 15th
1996
Weekday:
January code is 0 but 1996 is a leap year so subtract 1 ==> 6;
year 96 minus 3’28 is 12, code is 1:
6 (Jan in a LY) + 15 + 1 (year 96) = 22, shorten by multiples of 7 (3*7=21)
gives 1
Monday.
Turning 80:
Work out which day is always 2 days later:
Monday and 2 days later is a Wednesday.
This year (year 13 in 20xx; code is 2-1=1)
January, 15th
2013:
0 (Jan) + 15 + 1 (year 13 in
20xx) = 16 shorten by multiples of 7 (2*7=14) gives 2
Tuesday.
100 years later:
Work out which day is always 1 day before:
Monday and 1 days before is a Sunday.
