Why we ask for the place: the hour pillar is set by true solar time, not by the clock on the wall. Two people born at the same clock time in Madrid and Beijing are more than an hour apart in solar time. If a calculator never asks where you were born, its hour pillar is a guess.
Solar terms are computed astronomically from the sun’s apparent longitude, not from a fixed calendar date, so births near a term boundary land in the right month. For reflection, not prediction.
BaZi reads a birth moment as four pillars — year, month, day and hour. Each pillar holds two characters: a heavenly stem above and an earthly branch below. Eight characters in total, which is what ba zi means. Every character carries one of five elements and a yin or yang polarity, and a reading works with how they support and control one another.
The stem of the day pillar stands for the person. Everything else is read in relation to it — which characters feed it, which drain it, which it controls. That relationship is what the ten gods name. A Direct Wealth character is not wealth itself; it is the thing your day master takes hold of.
Clock time is a political convenience. A whole country runs on one standard meridian, so anyone living east or west of it is out of step with the sun. Spain sits west of Greenwich but keeps Central European Time, putting Madrid about 75 minutes behind the sun. Xinjiang keeps Beijing time and runs more than two hours out. The hour pillar follows the sun, not the clock.
Some calculators handle this properly and some never ask for a birthplace at all. If a tool only wants a date and a time, it cannot place the hour for anyone born away from their standard meridian — and that is the single most common reason two sites hand you different charts. We go through all the reasons here.
The month pillar changes at a solar term, the moment the sun reaches a particular apparent longitude. That moment drifts by hours from year to year, so a fixed calendar date gets it wrong for anyone born close to a boundary. This calculator computes the sun’s position for the actual date, which is the only way to place those births correctly.
The tradition is shared across East Asia — saju in Korea, bazi in China, shichu suimei in Japan — and the calculation is the same. Only the vocabulary differs. This calculator computes solar terms from the sun’s apparent longitude rather than reading them off a table, and it asks where you were born because the hour pillar depends on it.