How your chart is computed

The rules, named

Charts are cast with the open-source iztro engine, following the standard classical placement rules of Zi Wei Dou Shu: Life Palace from lunar month and hour, five-element bureau from the Life Palace's nayin, the fourteen major stars from the bureau and lunar day, and the four transformations (四化) from the birth-year stem using the standard table. The engine's code is public, and every placement is covered by automated tests. The engine follows the San He (三合) school's standard placements and the common ten-stem four-transformations table; other lineages differ on some assignments (notably the 庚 stem), which is a school difference, not an error. The engine's test suite is public.

github.com/SylarLong/iztro · tests

A worked example you can check

Take this birth: solar 15 January 1995, male, Wu hour (11:00-13:00) - lunar year 甲戌, twelfth month, fifteenth day. Any reference book, any teacher, any calculator should agree on the following:

• Life Palace at Wei (未); Body Palace joins it (a Wu-hour trait)
• Five-element bureau: Earth-Five (土五局)
• Emperor Star (紫微) and Heavenly Minister (天相) in Chen (辰)
• Heavenly Secret (天機) and Great Door (巨門), both bright, in Mao (卯)
• Military Music (武曲) and Heavenly Treasury (天府) in Zi (子)
• Year-stem 甲 transformations: 廉貞化祿 · 破軍化權 · 武曲化科 · 太陽化忌

Cast this chart here and compare against any source you trust. The placements will match - and if you have your own chart from a master, cast your birth details and check ours against theirs.

Conventions this engine uses

Where lineages disagree, these are the choices made here: the Zi hour (23:00-01:00) is split at midnight, so 23:00-24:00 is late Zi (晚子時) on the same calendar date and 00:00-01:00 is early Zi (早子時) on the new day; lunar leap months follow the iztro convention; the year boundary follows the lunar new year. If your school reads these differently, your chart may differ - that is a lineage difference, not an error.