Chart engine verification report
“Our charts are accurate” means nothing unless it can be checked. This page states what was verified, how, the result, and what was not verified.
What was verified (four items, all independent)
We wrote a separate implementation of the classical placement rules from the Zi Wei Dou Shu Quan Shu, sharing no code with the engine (iztro), and compared it with the engine's output for: 1) the Life Palace branch (count from the birth-month palace back to the birth hour); 2) the Body Palace branch (forward); 3) the Five Elements Bureau (Five Tigers rule for the palace stem, then the Na Yin element of the Life Palace stem-branch); 4) the Zi Wei star position (divide the lunar day by the Bureau number, pad to a multiple, count the quotient from Yin, then step back for odd and forward for even padding).
Method
Random birth dates from 1930 to 2029 with random hours, charts generated by the engine and compared with the classical result. Leap months follow the Quan Shu convention. Special cases: end of lunar year, early and late Zi, leap 4th month, leap 2nd month (leap vs. non-leap), the window between Lunar New Year and Li Chun, and the extreme dates 1900 and 2099.
Result
2026-10-01: 3000 random samples — 0 mismatches in the Life Palace, Body Palace, Bureau and Zi Wei position; all special cases passed.
What this exercise found
Upgrading the script exposed weaknesses in the earlier check: it compared only the Life and Body Palaces; the Zi Wei position used a baseline table derived from the engine's own output (a regression guard, not an independent check); and the independent Bureau routine was written but never used. All four items are now independently compared. The check also covers the engine only, not the year-boundary convention — which is how we found and changed the default (see the conventions page).
What was not verified
Star brightness, the transformation tables, minor stars, decade and annual details, and differences between schools have not had the same independent verification. The true-solar-time module has its own assertions (historical daylight saving, date changes, equation-of-time magnitude, late Zi) but it is our own implementation. AI readings and encyclopedia text are outside this verification.
How to check it yourself
The verification script is maintained with the site. If you are a researcher or developer and want the script, samples and per-case results, contact us via the footer. If you find a chart that disagrees with another tool, send the (anonymised) birth data and we will investigate and publish the finding.
Q: Did you write the chart engine yourselves?
No. Charts use the open-source iztro engine with the lunar-javascript calendar. What we add is convention choices, true solar time and independent verification.
Q: Does a passing check mean every detail is right?
No. It means these four outputs match the classical formulas. See “What was not verified”.