Day Master (Rì Zhǔ)
It is the heavenly stem of the day pillar, representing the querent themselves. All ten gods in the entire chart are calculated based on it.
The heavenly stem of the day pillar, representing the querent themselves, also called "Rìyuán" or "Rìgān".
All ten gods in the entire chart are based on it: the Companion and Rival, the Seal, the Eating God and Hurting Officer, the Wealth, and the Officer and Seven Killing, all refer to "the relationship between the other stems/branches and the Rìzhǔ". Therefore, changing the Rìzhǔ changes the entire chart's ten gods.
The three criteria for judging the strength of the Rìzhǔ (gaining season, gaining place, gaining momentum) are all asking the same question: How much support does this heavenly stem have in this chart.
⚠️ This site lists these three criteria and all the numbers, but does not make a conclusion of "strong self/weak self" — That requires a specific school's stance; the same chart can yield opposite answers under different schools.