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Zi Wei Dou Shu vs BaZi: two Chinese systems, read from different things
BaZi (八字, the four pillars) and Zi Wei Dou Shu (紫微斗数) both start from the birth moment. One reads four pairs of characters; the other builds a chart of twelve palaces with stars in them.
The short answer
Four pillars against twelve palaces
BaZi writes the year, month, day and hour as four pairs of a heavenly stem and an earthly branch — eight characters — and reads them through the five elements: what is strong, what is weak, what a given year adds. Zi Wei Dou Shu fixes the same moment into twelve palaces, places the stars in them, and reads the palace each star lands in.
The two are separate lineages of one tradition and do not convert into each other. A BaZi chart is not a Zi Wei Dou Shu chart seen from another angle; the arithmetic behind them differs.
What each one is better at
BaZi is read in terms of the elements. Zi Wei Dou Shu is read in terms of areas of life: which palace, which star, which transformation.
The chart cast on this site is Zi Wei Dou Shu. The BaZi vocabulary appears here only in pages like this one, where the two are set side by side.
Which one you are looking for
For a BaZi reading — four pillars, the five elements, the strength of the day master — find a practitioner of that method.
Here the twelve-palace chart is cast and the reading written from it: palaces, stars, transformations, the decade.
All readings See a completed reading first Cast your chart first — free
Questions
Do the same birth details give both charts?
Both are computed from the same date, hour and place, and they are different computations: the readings come out in different vocabularies about different things.
Why does this site use Zi Wei Dou Shu?
It is the method the readings here are written in, and the method read by the person who signs them.
Is one of them more accurate?
They answer different questions. What a reading can be judged on is whether it describes you; a full one is on the sample page.