Learn the day of the week of any date

If you are not familiar with memory techniques, you might not fully understand what’s going on here, in case, you might like to have a look on the wiki of mnemotechnics.org.

The technique is well known by memory guys. It consists in summing up 3 values and take the remainder of the euclidian division by 7.

For example, for 12 february 1945

  1. 19 =  7*2+5   => 5 (euclidian remainder)
  2. February   => 4 (learned association, explained after)
  3. 1945   => 6 (learned association, explained after)
  4. 5+4+6 = 15 = 2*7+1 => 1 (sum of the previous numbers, and euclidian remainder)
  5. 1=>monday (index in the week)

12 february 1945 is a monday

Explanation :

  • First step : a simple euclidian division, you take the remainder. ( e.g 21=7*3+0 => 0 ; 3=7*0 + 3 )
  • Second step : based on a learned association (January=1 ,February=4, march=4, avril=0, may=2, june=5, july=0,august=3,septembre=6,octobre=1,novembre=4,decembre=6).  Not so hard to learn if you use your memory system.
  • Third step : based on a learned repartition of all your numbers (0→99) in 7 rooms of your date palace. (check the following map at the end to know the repartition, I am too lazy to rewrite it for the moment. This is the hardest part.
  • Fourth step : add all the stuff up and as step 1, take the remainderof the euclidian division by 7.
  • Fifth step : add your day code.  As I am a french I prefer by convention that weeks start on monday so 1 is monday, 2 is tuesday, etc…. If you want to start your week with sunday, adapt your date palace by subtracting 1 to each of the location related digit (unless 0 which becomes 6).

Aaaaand the map is in french, sorry about that.


I used VUE (visual understanding environment) software  to build this. It helps me to review. Of course this map is dull and only display basic informations to mentally review my palace. In my mind it corresponds to real places and real interactions between my numbers (the numbers are associated with people I know).

Notes :

  • If you got  leap years (when the year can be divided by 4, like 88), you have to substract 1 from your final result if and only if the month is january of february.
  • If it’s another century than the XXth century, you have to add at the end a century code : 2 for 1800→1899 and 6 for 2000→2999.
  • To find the century code of another century, add 5 to the previous one. Unless it’s century leap year like 2000, 2400, 2800 …. in which case you add 6 instead. For example, century code for 2200→2299 is 6+5+5=16 which can be replaced by 2 (because 7*2 + 2 = 16). Of course there is a formula to compute the century code of any century. Have a look at the end of the post if you dare.

Let’s take a final example of a leap year in the XXI century :
15 january 2004

  1. 15 = 7*2+1 => 1
  2. january : 1
  3. 04 : 4
  4. sum = 6
  5. [leap year step] = 6-1 = 5
  6. [another century step] = 5 + 6 =11
  7. final result 11=7*1+4 => 4
  8. day : 4=>Thursday

Notice for centuries far from XIX. Let’s take 1900-1999 century for an example :

  1. 19 = 4 * 4 + 3 (dividend of the euclidian division by 4)
  2. 19*5=95 (multiply the century by 5)
  3. 95+4=99 (add all the stuff)
  4. 99+6=105 (add 6)
  5. 105=7*15 + 0  (euclidian remainder, the century code is 0)

To avoid big numbers, note that you can simplify early your expressions. You can do instead :

  1. 19 = 4 * 4 + 3 (dividend of the euclidian division by 4)
  2. 19*5=95 can be replaced by 5*5=25 (because 19=7*2+5) and 25 can be replaced by 4 (because 7*3+4=25
  3. 4+4+6=14 (add all the stuff, add 6)
  4. 7=7*2+ 0  (euclidian remainder)

artificial memory palace based on video games

This post may only interest people with knowledge on loci method (or memory palaces), if you don’t know about these techniques, please have a tour on mnemotechnics.org especially on the wiki 

As suggested there artificial memory palaces can be built from video games. As far as I know, there are two lazy options to get fresh locis :

- Maps of video games ( this website has a lot :  http://vgmaps.com/ ). If, like me, you are fond of zelda ocarina of times, you might find  these maps very interesting. It might provide huge resources, I learned Pi to its 1000th decimals (not sure I remember perfectly though) using less than 10% of the maps.

- Video of video games : It might be a good option if you don’t find the map you need and even more handy if you want to use journeys on the fly.

I tried with mario N64 (because I did not find maps on http://vgmaps.com/) and I picked this amazing speed run. Side note : Speed Runners are such crazy beasts… They should try memory palaces, they have the mental and the material to outperform us.

Here is my workflow : I used evernote+skitch to annotate (in a very rudimentar way) my set of locis. Then to reproduce it…you need evernote+skitch.  Screenshots are at the bottom of the post.

First I divide my screen in two, my attention is divided. I try to find good mnemonics images for my learning material when the video is not interesting (even if it’s rare), and when the video is about to reveal interesting place, I pause,  I push F10 (my shortcut to take a partial screenshot), I push some arrows pointing to the position of my mental images, I save. Life is too short to add extra informations, but skitch is ideal if you want to add extra stuff (like the aimed content for example). After the session, you might find useful to export all the stuff in a unique html file ( select your notes from evernote, file>export>export as a single web page). At the end you have something like this .  If, like me, you only use arrows, don’t forget to review as soon as you finish your session.

locisDivide your screen in two parts




When an interesting place is showing up, pause, screenshot and annotate with skitch.