Mentally calculating the day-of-the-week for any date in history sounds like an impossible task for a normal person, but the algorithm is actually pretty simple to learn.<p>Although there are tutorials for this elsewhere online, and little quizzes available, there didn't seem to be anything well optimised with multiple practice modes etc.<p>I originally created a basic version of this just for myself, but a small group of friends and family found it interesting and gave suggestions such as the daily game.<p>Multi-lingual support is a bit rudimentary at the moment, it will only translate the month names and weekday names, not other text. If any translation mistakes are identified please let me know.<p>Other feedback is welcome too.
Dividing by 7 is also a cool trick and it’s way easier than this.<p>1/7th is 0.142857 recurring. All you need to remember is one-four-two-eight-five-seven. Say it over and over. It’s my favourite number.<p>The magic: to get 2/7, 3/7, <i>any</i>/7, just move the decimal point:<p>- 2/7: 0.285714285714…<p>- 3/7: 0.428571428571…<p>- 4/7: 0.571428571428… (I’m typing these out but ‘from memory’ but not really: only by knowing 1-4-2-8-5-7)<p>- 5/7 & 6/7: left as an exercise for the reader.<p>So then the trick is to play a bit of mental magic. Pretend like this is really hard and that every decimal point is stretching your mental capacity to its very edge.<p>31/7? That’s 4, with 3/7 left over. Say it out loud as you gaze in to the middle distance and do this difficult, difficult calculation in your head: “four point four two eight five seven … one four … two eight five … seven one four …” and so on.<p>A fun trick which is very occasionally practically useful.
First question was “08/10/2023”<p>The majority of the world uses little endian, so the 8th day of the 10th month of the 2023rd year. 8th October is Sunday, as I know that because it’s the same day as 9th of May.<p>However experiments E has told me that much of the internet uses the minority American view of “middle endian”<p>Probably worth making it clear.
I've found the Month's First Sunday method[1] (a mild simplification of the Doomsday Algorithm including the odd-plus-eleven innovation) easiest, fastest, and most practical. I'm not insisting on it, just great for me, and I wish it were better known.<p>[1]: <a href="https://firstsundaydoomsday.blogspot.com/2011/01/learn-by-example.html?m=1" rel="nofollow">https://firstsundaydoomsday.blogspot.com/2011/01/learn-by-ex...</a>
My seven year old thinks I have superpowers now. Needless to say, I’m a big fan - it’s pretty amazing to go from learning to applying as quickly as I did. Great job!
This looks easier to memorise than another method: <a href="https://en.wikipedia.org/wiki/Doomsday_rule" rel="nofollow">https://en.wikipedia.org/wiki/Doomsday_rule</a><p>Nice work on the site!
Can you add more detail on the year table at the very bottom / how you're meant to use it? I can memorise it but I'm not sure how you're meant to use it after that.
> Mentally calculating the day-of-the-week for any date in history sounds like an impossible task for a normal person ...<p><pre><code> $ cal <month> <year>
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And look :-)