A Gnomon is the center of the Sundial. Teridax had one under the Coliseum, seen in BIONICLE 2: Legends of Metru Nui. There was also a Sundial on Mata Nui, in the depths of Onu-Wahi. Nixie found the Gnomon of this sundial in the foothills if Mt. Ihu, and later gave it to Takua, who inserted it into the sundial; upon using his lightsone to create a shadow on the four-o'-clock mark, the sundial opened, revealing a path into the depths of Makuta's lair.