One Way to Mentally Calculate the Day of the Week

quick, what day of the week is Halloween this year?


since i’m super bored, let me talk about a way to calculate what day of the week any given date is. thanks to the annoying Gregorian calendar, we pretty much never know this for more than a few days at any time, which no doubt wastes $900 quadrillion every year in world productivity.

so here’s my method!

given a date, first i figure out what day number in the year it is. consider Feb 1st: that’s day 32, because there’s 31 days before February, and Feb 1st is the next day after that. so for each month, i need to know the number of days in the year before that month begins. for March, it’s 31 + 28 = 59, and so on:

  1. Jan: 0

  2. Feb: 31

  3. Mar: 59

  4. Apr: 90

  5. May: 120

  6. Jun: 151

  7. Jul: 181

  8. Aug: 212

  9. Sep: 243

  10. Oct: 273

  11. Nov: 304

  12. Dec: 334

so when i see “Oct 31st”, i immediately convert “Oct” into 273, and then add 31 to it to get 304. that means Halloween is the 304th day of the year (305th in leap years).

the month shortcuts are pretty easy to memorize because it’s close to counting by 30s.

some methods, instead of having you memorize month shortcuts, have you memorize this instead:

  1. Jan: 0

  2. Feb: 3

  3. Mar: 3

  4. Apr: 6

  5. May: 1

  6. Jun: 4

  7. Jul: 6

  8. Aug: 2

  9. Sep: 5

  10. Oct: 0

  11. Nov: 3

  12. Dec: 5

these are month offsets. they’ve just taken out all the whole weeks before each month, so that after you add the day of the month, you won’t have to divide a giant 3-digit number by 7—at most, it’ll be a number in the 30s. but i like using day numbers in the year, because since i’ve already done this much work, sometimes it’s useful to figure out the number of days between two dates. you decide which method you prefer.

after figuring out the day number, i need to know how many days more than a whole number of weeks that is. consider day 45 (Valentine’s Day): that’s 3 days more than six whole weeks. so you’re subtracting the biggest multiple of 7 that’s smaller than the day number, and keeping what’s left over. for later months, it can help to have the multiples of 7 memorized all the way up to 7 × 52 = 364. (if you’re still reading this, you can probably do long division in your head easily, but shortcuts still help.)

the number left over corresponds to a day of the week. 1 = Monday, so 3 = Wednesday.

last, i need to know what day of the week the given year started on. the best case is if Jan 1st was a Monday, because if so, the answer from the previous step would be the final answer. but 2019 started on a Tuesday, so each day actually occurs 1 day of the week later than calculated in the previous step. so for any date in 2019, i need to take my previous answer and add 1, getting 4 = Thursday for Valentine’s Day.

i call that a year offset of 1. the offset is the number of days between Jan 1st and the Monday before it. if Jan 1st itself was a Monday, the year offset would be 0; if it was a Sunday, the offset would be 6.

each year has a different offset, which you just have to memorize. given the offset of any one year, you can calculate the offset of any other year, but even i don’t bother with that because it’s a pain in the ass. (it’s because 365 days is 52 × 7 + 1, so each year’s offset is 1 higher than the previous year’s, or 2 higher if the previous year was a leap year—so you need to have the leap year rules memorized too.)

in conclusion, it’s two parts: first, figure out the day number, and second, figure out what day of the week that is, which includes the shift for the date itself, and the shift for the entire year.

and that’s it! now you can use this trick to impress absolutely no one!

Why the Korean Keyboard Layout Is Brilliant

five hundred years ago, the Korean writing system was specifically designed to be easy to learn. similar sounds are written with similar characters, and related sounds have consistent patterns. some characters are actually pictures of the way your mouth pronounces them. seriously, check out this video and come back when you’re done.

many years later, the Korean keyboard layout seems to have been designed according to the same philosophy.

1 - keyboard with letters.png

(don’t worry, i’ve written this article so that people with minimal knowledge about Korean can understand it.)

consonant–vowel split

the first thing you’ll notice is that the left hand takes all the consonants and the right hand takes all the vowels. you can’t do this with English, but you can with Korean, because it happens to have a similar number of consonants and vowels: 14 of each, not including combinations.

the vowels yae and ye are then placed on Shift modifications of ae and e, which fits all the letters onto 26 keys, just like in English. and because Korean uses roman-style rather than Chinese- and Japanese-style punctuation, this allows the punctuation keys to remain unchanged between Korean and English, making it easy to switch between the two.

splitting the keyboard into consonants and vowels not only makes it easier to remember, it also causes good hand alternation, which makes typing faster because while one hand is hitting the current key, your other hand can start reaching for the next one.

the one exception to the consonant–vowel split is that yu is a vowel, but it’s placed on the B key, the rightmost key typed with the left hand.


twin consonants

5 of the consonants have “twin” versions, not included in the individual 14: b j d g s and bb jj dd gg ss. twin consonants are “tense”, pronounced with more stress than their plain counterparts. (official romanizations differ slightly.)

the twin consonants are placed on Shift modifications of their plain counterparts, and these are placed on the first 5 keys on the upper row, which is easy to remember.

2 - twin consonants

if you’re curious, the twin consonants couldn’t be typed by hitting their plain versions twice in a row, because that would cause ambiguity: you wouldn’t be able to differentiate between one syllable ending with s and the next syllable starting with s too, versus just ss at the beginning of the second syllable.

aspirated consonants

4 of the consonants have aspirated counterparts, included in the individual 14: b j d g and p ch t k. see how they sound similar? aspirated consonants have an extra burst of air, which you can feel if you hold your hand in front of your mouth while saying p versus b, for example.

the aspirated consonants are placed on the first 4 keys on the lower row, and they correspond with the first 4 letters on the upper row.

3 - aspirated consonants

for some reason though, the aspirated consonants go in reverse order of their plain counterparts; i haven’t thought of a good reason for this. if they had gone in the same order, you would have been able to use the same finger for related pairs, like b and p, j and ch, and so on.

4 - aspirated directions

the consonant s has a twin version, but no aspirated counterpart, so that’s why it’s the 5th key in the upper row; it’s in the group of 5 twin consonants, but not in the group of 4 aspirated consonants.

that leaves just 5 more consonants, which don’t have any counterparts: m n (empty) l h. these are placed on home row.

5 - all consonants


horizontal and vertical vowels

Korean vowels are written as long horizontal or vertical lines with short perpendicular marks. each syllable block can have either a horizontal vowel, a vertical vowel, or a horizontal vowel followed by a vertical vowel.

6 - vowels.png

on the keyboard, horizontal and vertical vowels are grouped separately.

7 - vowel groups

merely separating the two groups of vowels makes them easier to remember, but the key is that the vertical vowels are above and to the right of the horizontal vowels.

this exactly follows how syllable blocks are written when they have two vowels, meaning the keys are arranged spatially. this has a remarkable effect: when you type Korean, you feel like you’re tapping directly on the letters where they appear in the syllable block.

8 - spatial 1
9 - spatial 2.png
10 - spatial 3.png

there are only so many possible vowel pairs, and they all start with one of o u eu and end with one of eo a i ae e. in all these pairs, the second vowel is placed above or to the right of the first vowel, and because all consonants are on the left too, the keys you type are all roughly mapped to their final positions in the syllable block you’re typing.

it really is a cool feeling.

direction of vowel markings

the horizontal and vertical vowels are then divided into subgroups. for the horizontal vowels, vowels with short marks above the long line are placed above, and vowels with marks below are placed below. likewise for the vertical vowels: vowels with marks to the left are placed to the left, and vowels with marks to the right are placed to the right.

this further makes the layout easier to remember and feel more spatial when you type on it.

11 - vowel marking directions

it’s not perfect—ae and e are exceptions, although it’s easy to remember those two as a separate group because they’re the only vowels written with two long lines.

i also wish that i were in between eo and a. since i has no mark, it would fit perfectly between eo with a left mark and a with a right mark. this would have broken up a and ya next to each other though.

number of vowel markings

finally, vowels with two marks are placed further away than their one-mark counterparts. two-mark vowels are pronounced the same way, just with a y- sound before them.

again, this makes the layout easier to remember, and it’s also practical because the y- vowels are less common than the regular vowels. and also again, ae and e are exceptions; their y- counterparts are on Shift modifications.

12 - vowel marking number


do you remember how long it took you to learn to type in English? Qwerty is nonsensical, not grouped by letter type in any way. the vowels are scattered, and good luck finding any relationship between D and T, or G and K, for example—most English speakers aren’t even aware of the relationships between these sounds, because the letters don’t indicate them.

logical grouping makes the Korean keyboard layout remarkably easy to learn. most people who learn it won’t analyze in such detail, but they’ll benefit from somehow being able to pick it up easily, and experience that unique feeling of spatially arranged letters.

the Korean keyboard layout follows the same philosophy as the Korean writing system: the easier something is to learn, the more people can make good use of it. these two systems were designed centuries apart, and yet they follow the same guiding principle. that, to me, is delightful and charming.

Clear Umbrella

clear umbrella

the only acceptable color for an umbrella is clear.

why would i want to block off almost half of my field of view? it feels restricting. isn’t it just nicer to see what’s around you?—and besides, there are views to be seen.

but clear also broadcasts the key feature of an umbrella: it’s waterproof. not all fabrics are waterproof; they have to be specific kinds, and usually treated with a coating. a clear canopy can only be made of plastic, which is an inherently waterproof material.

a clear umbrella makes its most functional aspect its most prominent one—a harmony of look and function. that’s good design.