What is Double-hour (Shi Chen)?

A double-hour (Shi Chen) is one of the twelve two-hour periods the old calendar divided the day into, named after the twelve Earthly Branches: Zi, Chou, Yin and so on to Hai. In Zi Wei Dou Shu, the double-hour is the most sensitive input: one double-hour earlier or later and the Life Palace moves a palace, turning all twelve palaces of the birth chart. So before casting a chart, converting your birth time to the right double-hour matters more than anything.

The short version:

• Formula: one double-hour = two hours; the Zi hour starts at 23:00, and a new double-hour begins every two hours, ending with Hai at 21:00–23:00.
• Setting the Life Palace: from the birth-month palace as the Zi hour, count backward to your birth hour for the Life Palace, forward for the Body Palace.
• Late Zi hour: from 23:00 to midnight, Xingge counts it as the Zi hour of the next day and moves the date too.
• Correct first: take off daylight saving; use the local clock time where you were born; true solar time is off by default.

The twelve double-hours

A time exactly on a boundary belongs to the later double-hour: 01:00 sharp is Chou, 07:00 sharp is Chen. The double-hours use the same branches as the zodiac animals, but your animal sign comes from your birth year and the double-hour from the moment you were born; the two are unrelated.

How the double-hour sets the Life Palace

Volume two of the Quan Shu says:

In general, everyone's chart starts the first month at Yin and counts forward to the birth month; then from the birth month, start the Zi hour and count backward to the birth hour to place the Life Palace, and forward to the birth hour to place the Body Palace.

Count from Yin as the first month forward to the birth month, then from that palace as the Zi hour, count counterclockwise to the birth hour for the Life Palace and clockwise for the Body Palace. So each double-hour of difference moves the Life Palace one palace over. The book goes on with examples:

If born in the first month at the Zi hour, place both the Body and Life Palaces in Yin; at the Chou hour, turn backward to Chou for the Life Palace and forward to Mao for the Body Palace; at the Yin hour, turn backward to Zi for the Life Palace and forward to Chen for the Body Palace.

By this method, for someone born in the first lunar month, the twelve double-hours give these Life and Body Palaces:

For other birth months the branches of the Life and Body Palaces shift with the month, but the last column stays the same: which palace holds the Body Palace depends only on the double-hour. People born in the Zi or Wu hour have the Life and Body Palaces together; Chou and Wei put it in Fortune, Yin and Shen in Career, Mao and You in Travel, Chen and Xu in Wealth, Si and Hai in Spouse.

One more example: born in the third lunar month at the Chen hour. Counting forward from Yin as the first month, the third month is Chen; from Chen as the Zi hour, counting backward to the Chen hour goes Zi at Chen, Chou at Mao, Yin at Yin, Mao at Chou, Chen at Zi, so the Life Palace is in Zi.

The special problem of the Zi hour: the late Zi hour

The Zi hour spans two days: 23:00 to midnight is the tail of the previous day, called the late Zi hour; midnight to 01:00 is the start of the new day, called the early Zi hour.

Schools differ on whether someone born in the late Zi hour counts as born that day or the next. Xingge follows most charting software and treats the late Zi hour as the Zi hour of the next day, moving the date to the next day as well; some teachers count it as the same day. Once the date moves, the lunar day changes by one and Zi Wei's position can change with it. When comparing apps, this is one of the most common differences.

Leap months

Zi Wei Dou Shu uses lunar months. For people born in a leap month, the Quan Shu says:

Those born in the leap first month should place the Body and Life Palaces within the second month.

That is, a leap month always counts as the next month. A common modern method counts days up to the fifteenth of the leap month as the previous month and the sixteenth onward as the next; Xingge uses the latter. Born on the tenth day of a leap fourth month, you're charted as the fourth month; born on the eighteenth, as the fifth.

Correct the birth time first

The time on a birth certificate is what the clock showed then, and it may need correcting before casting a chart:

• Daylight saving time: if daylight saving or a wartime clock change was in force where and when you were born, the clock was an hour ahead of standard time, and that hour has to come off first. Born at 07:30 during daylight saving, for example, the standard time is 06:30, which moves the birth hour from Chen to Mao and the Life Palace by one.
• Use the time where you were born: the mainstream practice in Zi Wei Dou Shu is to use the local clock time at your birthplace, without converting it to another city's time. Born at 10 a.m. in New York means 10 a.m.
• True solar time: adjusting the clock time to where the sun actually was, using your birthplace's longitude. Schools disagree and the classics don't do it; Xingge doesn't use it by default, but you can switch it on.

Xingge takes out daylight saving automatically, and all its time rules are on How Xingge casts a chart.

Boundaries and unknown birth hours

• Born near a boundary: for example, born at 08:55, five minutes from the line between the Chen and Si hours. Birth times often carry a few minutes of error, so both charts are worth reading; pick the one that reads more like you. When your birth time is within fifteen minutes of a boundary, Xingge reminds you the other double-hour is possible too; that includes midnight, since the late and early Zi hours fall on different days.
• Unknown birth hour: you can use a birth-hour questionnaire to find the most likely answer, or work back from the Body Palace: it only lands in six palaces, so ask yourself whether you've put the most effort into work, love, money, the wider world, your inner life, or simply staying yourself, and compare with the table above. Read an estimated chart more loosely.

The double-hour fixes the Life Palace, and the Life Palace in turn fixes the Five Elements Bureau, the Life Master and where the Decade Luck begins, so one wrong double-hour shifts everything after it.

The full casting steps are in the lesson how your chart is cast. Enter your birth time and draw your chart; the converted double-hour is shown on the chart.