Why saju apps give different results

01

What did the clock say in Korea then?

The standard time and daylight saving time Korea used on the day of the birth are applied as they were.

Korea used daylight saving time in the summers of 1948–1951, 1955–1960 and 1987–1988. Daylight saving time moves the clock one hour ahead in summer. From 1954 to 1961, standard time was UTC+8:30, half an hour behind today's.

For example, 10:00 am in July 1987 is 9:00 am on today's clock. Miss this, and the Hour Pillar can change. Near midnight, the Day Pillar can change too. This site finds that day's offset in the international time zone data (IANA tz, old records included).

On this site"UTC offset used" under "How this was calculated" is this value. A birth at a daylight saving time change is flagged when you enter it.

02

Why take about 30 minutes off the birth time?

Korean standard time is set for 135° east, so in Seoul (about 127°) the sun runs about 32 minutes behind the clock. So the site takes off that much.

The Hour Pillar is a two-hour slot of the sun's position. So this site reads it from the clock corrected for the birthplace's longitude (local mean time): -32 minutes in Seoul, -24 in Busan.

Some apps skip this correction. Born just after an odd hour, like 1 or 3 o'clock? Apps may give different Hour Pillars. Some apps use true solar time. The sun's highest point shifts through the year, by up to about 16 minutes. True solar time corrects for this too (the equation of time). This site uses local mean time.

On this site"Time correction" under "How this was calculated" gives your birthplace's minutes. Within 15 minutes of a slot boundary, the result also names the neighbouring Hour Pillar.

03

Born after 11:00 pm: which day is it?

Corrected 23:00–24:00 keeps that day's Day Pillar; only the Hour Pillar's stem is taken from the next day.

The Rat hour runs from 23:00 to 01:00 in corrected time. Some schools change the day at 23:00, others at midnight. This site changes it at midnight of the corrected time (about 00:32 in Seoul, in today's standard time) by default (the split between late and early Rat hour).

If you were born in this hour, you are asked which reading to use when you enter it, and the choice is shown under "How this was calculated".

On this site"Rat hour rule" under "How this was calculated" is this choice.

04

When do the saju year and month change?

The year changes at Ipchun (the start of spring), not on 1 January or the lunar new year, and each month at a solar term, not on the 1st.

Saju months start at 12 of the 24 solar terms, which divide the sun's path (Ipchun, Gyeongchip, Cheongmyeong …). The Year Pillar also changes at the moment of Ipchun.

So a birth before Ipchun, in January or early February, belongs to the previous year. Its zodiac animal and Year Pillar are that year's. If you were born within an hour of a solar term, we tell you when you enter it. We also tell you if the time is unknown and a term began that day. The term times come from an astronomical library (lunar-javascript).

On this siteYour Year's months are these solar-term months, so "November" starts around 7 November (Ipdong), not on 1 November.

05

Why does the Useful God differ between apps?

There are several ways to choose it, and this site uses strength balancing (eokbu) by default. For its judgements, the site follows one classic, the Di Tian Sui Chan Wei (滴天髓闡微).

The Useful God is the element that balances a chart. Methods such as strength balancing, climate (johu), mediation, illness-and-medicine and structure can give the same chart different Useful Gods, and then the "good years" can be the opposite. Even within strength balancing, books and schools judge differently. This site follows the Di Tian Sui Chan Wei, Ren Tieqiao's (任鐵樵) commentary on the Di Tian Sui, with real charts as worked cases. Follow another commentary on the Di Tian Sui, such as Xu Lewu's (徐樂吾), or another school, and the Useful God can differ.

First, this site weighs the seven letters other than the Day Master. The month's bottom letter (Month Branch) counts most. Then it finds the share that supports the Day Master (Peers and Resource). At 0.50 or more, the Day Master is strong. At 0.35 or less, it is weak. In between, three more things are checked: whether the birth season supports the Day Master (deungnyeong; the last month of each season, an Earth month, counts as part of that season), whether the main Hidden Stem of the Day Branch does (deukji), and whether more than half of the other letters do (deukse). With two or more of the three, the Day Master is strong; otherwise it is weak. So the verdict never leaves a chart in the middle as balanced.

A fixed strength-balancing table then picks the Useful God. A winter chart short of Fire, or a summer chart short of Water, adds a climate element (johu). But if that element restrains the balancing pick, the balancing pick stays. A follow structure is used only when one side is very strong or very weak. Mediation, illness-and-medicine and structure methods are not used. They rest on the reader's judgement, so code cannot apply them the same way to everyone.

These rules were tuned against the worked cases in the Di Tian Sui Chan Wei. The rule for an unknown birth hour has not been checked against the book's cases.

On this site"Useful God" under "How this was calculated" gives your chart's Useful God and why, in one line. The yearly graph's scores stand on it.

06

What is the calculation based on?

Public data and general saju principles, with every rule stated on this page and under "How this was calculated".

If another app still disagrees, check its time correction and Rat-hour rule first. That is where most differences come from.