Did you ever want to know exactly what day a certain date corresponded to?
It's a skill that seems to vastly impress people. Here is a formula
I discovered which does the trick. I need paper to do it, but maybe
*you *can do it in your head.

You will need:

- A starting date, eg., January 1, 2002 was a Tuesday
- To remember the following menmonic 303 232 332 323 which represents the different lengths of months in a year. This is the hardest part.
- To be able to do septal(base-7) arithmetic

Steps:

- Given the days of the week are numbered like this: 0=Sun, 1=Mon, 2=Tue, 3=Wed, 4=Thu, 5=Fri, 6=Sat (this is highly intuitive for me, I hope it is for everyone.)
- Add digits from the mnemonic beginning at the month you began in, up to but not including
the month you want, for example, if you pass from FEB to APR, add 0+3 (3
**03**232 332 323.) - Subtract your starting day from the day you want, in base-7.

ex1. Given February 6th is Wednesday(3), what is April 17th?

Feb to Apr add (0+3=3) 3ex2. Given January 1st, 2002 is Tuesday (2), what is August 22nd?03232 332 323,

3 + 0 + 3 = 6

date 17th - 6th = 11, 6+11 = 17 = 3_{7}, Therefore,

April 17th is Wednesday (too).

Travel through JAN FEB MAR - APR MAY JUN - JUL =ex3. Given April 30th is Tuesday(2) what is May 7th?303 232 3

2 + 3+0+3 + 2+3+2 + 3 = 18 or 4_{7}

22 - 1 = 21 (note, 21 is 0_{7}) so Aug 22 is Thursday(4).

April30 to May30 is 303

date 7-30 = -23, -21 is 0

4+5=9 or 2