It doesn't predict. It holds up a light.

You have probably typed your date of birth into something, somewhere, on a day when you felt stuck. What comes back is usually three or four lines, like the daily horoscope in the corner of a sports paper. Someone who knows a little saju, meanwhile, walks away with material of an entirely different depth. This service began because that gap bothered me. The aim was to let anyone look back at where they stand — without knowing the vocabulary, even if this whole culture is new to them.

Of course, as technology improves, the gap will keep narrowing. But wherever a threshold is lowered, a paid product tends to appear and build a new tier on top of it. So I don't think this service will become pointless any time soon.

So I set one rule at the start. It will not try to predict.

No words that frighten

There are phrases like "such-and-such a sal (煞) hangs over you." Samjae (三災), sal, hyeong and pa (刑破) are words in common use in saju reading, and this service, too, looks at the combinations and clashes among the characters (合沖) in its calculations. But I decided not to use those words as grounds for misfortune.

The world already holds enough to be afraid of. Live long enough and a day comes when, out of nowhere, you have to eat a frog. Telling someone at that moment, "several more frogs this size are waiting for you," is not going to move anyone.

Instead, it observes three things, in order.

• Dry and wet (燥濕) — what state is the water in — the first condition for anything to live?
• Cold and warm (寒熱) — is the temperature of that place kind to life, or not?
• Empty and full (虛實) — on that ground, does the day master (the one character that stands for you in the chart) stand firm, or is it fragile?

It is the order a probe follows on reaching an unfamiliar planet: look for water first. And it speaks of what is there before what is missing. Faced with a tree on frozen ground in midwinter, it does not stop at "it is cold." It first writes, "It has shed every leaf and drawn its strength into its deep roots to endure." The missing sunlight comes after that — and even then as a question: "where the warmth to thaw these deep roots might be." This is not consolation. It is describing the landscape as it is.

I imagined a dial lock

At first I wanted the moment a chart settles to feel like a finely made dial lock on a suitcase — a puzzle clicking into place. But for a beginner who had only heard that web pages are made of HTML, there was no way to build what I imagined. Columns of characters rolling and then stopping with a snap was the best I could do at the time.

Once it was built, I saw that it looked like a slot machine. The moment the reels roll, a user takes it for a lottery. The calculation gives the same result every time for the same birthday, yet the staging was saying "a draw, left to luck." So I reset the aim: not the feel of drawing a lot, but of coordinates falling into place — a telescope coming into focus, an orbit catching. The old look is still there on the screen.

For the same reason, nothing random goes into choosing the picture. It is picked by a value fixed by the date and hour of birth, so the same birthday and hour bring up the same picture no matter who opens it. When the month turns with the solar terms, the picture sometimes moves along one place — and that, too, follows the solar terms, not a draw.

The stems as signs, the branches as nature

Hover over a character, or tap it with a fingertip, and a small picture appears. The ten Heavenly Stems are drawn only as flows of energy, in white chalk lines on deep blue. 甲 splits as it rises, 丙 spreads in every direction, 庚 is made to look like a solid crystal. The twelve Earthly Branches, by contrast, are deliberately concrete images from nature. The energy of the sky is abstract; the seasons on the ground are scenery you can see.

The decision I like best is 子. 子 usually calls up water, but here it is drawn as a seed underground that has not yet sprouted — the seed handed down from 亥 just before it, lying buried. Only then do the twelve, set side by side, read as the story of a year: a seed sprouts, grows, bears fruit, and returns to seed.

Two wishes

While making this I held two wishes. One was a light comfort, about the weight of a four-leaf clover laminated at a street stall and slipped into a wallet. The other was the solid feeling of a tattoo. The two pull in opposite directions: make it light and the weight goes; make it heavy and a threshold appears.

So I split them into layers. The image lets you feel it without knowing anything (access); the Chinese characters carry the old mystery (weight); the numbers sit where only those who want them will look. Every screen is tested with one question: does this keep both?

Not becoming a service that predicts meant, in the end, giving up a few things: prophecy, frightening words, the thrill of the draw. What remained is a coordinate. Where you were standing — that I can show you, as a picture. Where you should go — that I will not.