Methodology
How Purple Tome Casts a Zi Wei Dou Shu Chart
Updated
Every Purple Tome chart is cast by a deterministic engine that follows one documented set of classical rules: the standard star placement of the Zi Wei Dou Shu Quan Shu tradition and the Ni Haixia (倪海厦) Tian Ji table for the Four Transformations. This page lists those rules in full, so any chart can be checked against them.
The rules, one by one
| Calendar | Your Gregorian birth date is converted to the Chinese lunisolar calendar. The year changes at Lunar New Year, not on January 1. |
| Leap months | A birth in a leap lunar month counts as the previous month for days 1–15 and as the following month from day 16 on. |
| Birth hour | Clock time is converted to true solar time at the birthplace (historical daylight saving, longitude, equation of time), then to one of twelve two-hour periods. |
| Birth date | The date that true solar time falls on is the chart date. A true solar time of 23:00–23:59 (the late Rat hour) is cast as the following day. |
| Unknown birth time | The chart is cast for the Rat hour of the entered date. Without a birth time, which palace holds which stars is a placeholder, so palace-level readings are much less reliable. |
| Four Transformations | Birth-year transformations follow the 倪海厦《天纪》 (Ni Haixia, Tian Ji) table below. Decade transformations use the stem of the decade palace; yearly ones use the stem of that year. |
| Ten-year periods | The first period starts at the age set by the element bureau (2 to 6) and moves clockwise or counter-clockwise depending on sex and whether the birth year is yin or yang. |
| Star placement | The 14 major stars, the lucky and harmful stars and the minor stars are placed by the standard rules of the 紫微斗数全书 (Zi Wei Dou Shu Quan Shu) tradition, computed with the open-source iztro library. |
The birth-hour and birth-date rules are explained with worked examples on the true solar time page.
The Four Transformations table
Each heavenly stem attaches the four transformations — Hua Lu (Prosperity), Hua Quan (Power), Hua Ke (Renown) and Hua Ji (Adversity) — to four specific stars. This is the table the engine uses, rendered directly from its source. Lineages agree on most rows; the 庚 (Geng) row is the one most often disputed.
| Year stem | Hua Lu | Hua Quan | Hua Ke | Hua Ji |
|---|---|---|---|---|
| 甲 | Lian Zhen 廉贞 | Po Jun 破军 | Wu Qu 武曲 | Tai Yang 太阳 |
| 乙 | Tian Ji 天机 | Tian Liang 天梁 | Zi Wei 紫微 | Tai Yin 太阴 |
| 丙 | Tian Tong 天同 | Tian Ji 天机 | Wen Chang 文昌 | Lian Zhen 廉贞 |
| 丁 | Tai Yin 太阴 | Tian Tong 天同 | Tian Ji 天机 | Ju Men 巨门 |
| 戊 | Tan Lang 贪狼 | Tai Yin 太阴 | You Bi 右弼 | Tian Ji 天机 |
| 己 | Wu Qu 武曲 | Tan Lang 贪狼 | Tian Liang 天梁 | Wen Qu 文曲 |
| 庚 | Tai Yang 太阳 | Wu Qu 武曲 | Tai Yin 太阴 | Tian Tong 天同 |
| 辛 | Ju Men 巨门 | Tai Yang 太阳 | Wen Qu 文曲 | Wen Chang 文昌 |
| 壬 | Tian Liang 天梁 | Zi Wei 紫微 | Zuo Fu 左辅 | Wu Qu 武曲 |
| 癸 | Po Jun 破军 | Ju Men 巨门 | Tai Yin 太阴 | Tan Lang 贪狼 |
A year takes the row of its stem: 2026 is a 丙 (Bing) year, 2027 a 丁 (Ding) year. See what 2027 means.
How the rules are checked
The Four Transformations table is tested against an independently transcribed classical source, not against the engine's own output. True solar time is tested on historical daylight-saving cases (the 1974 year-round daylight saving, the 2007 US rule change, Arizona) and swept minute by minute around midnight across fifteen time zones.
When a rule turns out to be wrong, the fix ships with a public note on the accuracy changelog. How the written reading is produced — and what the AI is and is not allowed to do — is on How it works.
Who makes it
Purple Tome is made by works on my machine LLC, a small independent studio, as an app for iPhone and Android with a free chart on this website. There is no human astrologer reviewing individual readings, and none is implied anywhere on the site.
Common questions
Which school of Zi Wei Dou Shu does Purple Tome follow?
Purple Tome places stars by the standard rules of the 紫微斗数全书 (Quan Shu) tradition and uses the 倪海厦《天纪》 (Ni Haixia, Tian Ji) table for the Four Transformations. Where schools disagree — most visibly on the 庚 (Geng) stem — it uses that one table consistently rather than mixing sources.
Why does my Purple Tome chart differ from another Zi Wei calculator?
The three usual reasons are true solar time (many calculators use clock time), the late Rat hour rule (some keep a 23:00–23:59 birth on the same day) and the Geng-year transformation table. Each is a documented choice on this page, not a random difference.
Is the chart calculated by AI?
No. The chart is computed by a deterministic engine — the same birth details always produce the same chart. AI is used only in the app to turn a computed chart into a plain-English reading, and it cannot add a star that is not in the chart. See How it works for the details.
Who makes Purple Tome?
Purple Tome is made by works on my machine LLC, a small independent studio. Chart rules are covered by automated tests, and corrections to the engine are published on the accuracy changelog with the date and what changed.
Every rule above runs when you cast a chart. Try it with your own birth details.
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