What are 대운 and 세운?
The ten-year chapter you are walking through, and the year you are standing in.
In plain words
The eight letters you were born with do not move. What moves is the weather they stand in. Saju splits that weather into layers: a chapter roughly ten years long (대운), the year you are in (세운), and the month (월운). Skilled readers weigh the ten-year chapter most heavily when they talk about timing, because a chart that is short of Water reads very differently during a Water decade than during a Fire one.
The word 운 here does not mean luck in the lottery sense. It means the run, the passage, the stretch of road you are on. A chapter that leans with you is easier to spend, and a chapter that leans against you is one you grow through. Neither is a reward and neither is a punishment.
How Bokki computes it
The decade chapters run in a direction, and the classical rule states it in two halves: yang birth-year stem with male, or yin birth-year stem with female, walks forward from the month pillar; the other two pairings walk backward. It is written that way in the sources, in a binary that does not describe everyone, and Bokki reports the rule rather than rewriting it. What we do refuse to do is guess: if that input is not given, we compute no decade chapters at all and say the field is empty.
The start age is measured on the calendar, not assumed. Count the days from your birth moment to the solar term that opens the next month if you walk forward, or back to the one that opened this month if you walk backward, then read three days as one year. Born 15 May 1990 at 14:30 walking forward, the next term is 芒種 around 6 June — about twenty-two days away, so the first chapter opens at roughly seven years and two months. Walking backward from the same birth, 立夏 was about nine days earlier, so it opens at about three years and two months. That is why two people born on the same day can be in different chapters at the same age.
From there the chapters step one pillar at a time, ten years each, forward or backward through the sixty-pair cycle. For 1990-05-15 walking forward the chapters read 壬午 at 8–17, 癸未 at 18–27, 甲申 at 28–37. Walking backward from the same birth they read 庚辰 at 4–13, 己卯 at 14–23, 戊寅 at 24–33. For each chapter Bokki names its element, its Ten God against your day stem, and whether its element is one your chart was short of. The years before the first chapter opens are left blank — we do not invent a pillar for them.
The year layer is simpler but has one trap in it. The Saju year turns at 立春, and 立春 is a moment, not a date — in 2025 it fell at 22:10 on 3 February, on the almanac's UTC+8 clock (23:10 in Korea). Bokki reads the year at that moment. We used to read it by date instead, and across 1990 to 2035 that produced one day every single year on which the card showed a year pillar and a month pillar that cannot legally stand together. The month layer turns on the solar terms in the same way, so a Bokki month never begins on the 1st.
What we do not compute
We read the upper letter of each chapter, not the lower one. The Ten God and the element we report for a decade or a year come from its stem alone. Traditional practice often reads the lower letter too, and looks at how it binds or clashes with the letters you were born with; Bokki does not compute that yet, so it does not talk about it.
We also do not model the seam between chapters — the years when one is closing and the next is opening — and we do not track the special stars into a decade or a year. Those readings exist and are real inside the tradition; they are simply not in our arithmetic, and we would rather leave a gap than fill it with something we did not compute.
And we do not turn a chapter into a forecast. Bokki will say whether a decade leans with you or asks more of you, and it will not say what will happen in it, when, or to whom. No dates on events, no numbers on a life, and nothing at all about what other people will decide.
Closing note — a direction, a start age, and a boundary the clock does not draw
In short: daeun is a direction (forward or backward through the sixty-pair cycle, set by the birth-year stem crossed with sex) plus a start age measured in days against a solar term and read at three days per year. The two directions from 15 May 1990 14:30 land on different chapters at the same age — 8–17 壬午 walking forward, 4–13 庚辰 walking backward — and both trace to a term about three weeks apart, 芒種 or 立夏.
We read only the upper letter of each chapter and its Ten God against your day stem — never the lower letter, never how it clashes with your birth letters, never the seam between two chapters. And 세운 turns at the moment 立春 lands, not the date: reading it by date instead produced one impossible year-and-month pairing every single year from 1990 to 2035, which is the bug this page's arithmetic exists to not repeat.