What does millstone mean in geomantic omen?

In geomantic omen, the millstone means "Qinglong", and in folk geomantic omen, the roller is called the white tiger.

Qinglong White Tiger is the God of the East and the God of the West in Han mythology. Star worship originated from ancient Han people. Among many door gods, there is a special door god, which is specially used to guard the Taoist temple gate. They are what Taoism often says: "Left green dragon, right white tiger". For example, in the Taoist resort Qingcheng Mountain Ancient Road View (Shi Tian Cave), in front of the towering mountain gate, there are two temples. The left temple is a mighty dragon statue named Meng Zhang Shen Jun, and the right temple is a brave white tiger statue, a famous prison soldier Shen Jun.