The elements inside the element
What are hidden stems?
A single Earthly Branch (your zodiac animal) is not one pure element. Each branch secretly holds one to three more elements inside it, called the hidden stems (藏干). So your animal's "main element" is really a small container of sub-elements. This hidden layer is where BaZi gets its depth: it roughly doubles what a chart carries, and it is why one animal can hold more than one element.
Each branch ranks its interior by strength: a primary element (the branch's own), a fading element left over from the season before, and sometimes a rising element belonging to the season ahead. Open any animal below and watch its inner elements appear.
Why it matters
The hidden layer does real work
It reveals what is concealed
Some parts of a chart, like the money role or the partner role (the Ten Gods), can sit only in this hidden layer, invisible on the surface. Read just the four visible characters and you see about half the chart.
It roots the self
Your Day Master is "rooted" and strong when a branch hides its own element. Judging strength depends on counting that hidden support.