What is Upper Trigram?

The top three lines (lines 4, 5, 6) of a hexagram. Also called the outer trigram (外卦). Traditionally associated with the external situation, the environment, or the other party. In Plum Blossom Numerology, it is the function (用) trigram.

Source: Meihua Yishu (梅花易數), Shao Yong