the Great Ultimate is depicted as an ellipsis with ten stations on its periphery… shows it as a blank circle. Daoist speculation made special use of Zhou Dunyi’s version and related it to alchemical
Kohn documents the multiple diagrammatic forms through which the Great Ultimate was visualized in Daoist tradition, from concentric circles to blank circles, each representing a distinct cosmological and alchemical theory.
, Daoism Handbook, 2000thesis