These included the astrolabe, quadrant, gnomon, celestial sphere, sundial, and compass. Similarly, the obelisk from Campus Martius was used as the gnomon for Augustus's zodiacal sundial. The spar of this particular bridge forms the gnomon of a large garden sundial. On some sundials, the gnomon is vertical. Both appear to be sundials with gnomon curves etched on a flat surface. Its gnomon was an obelisk from Heliopolis. Shen is credited with making improved designs of the gnomon, armillary sphere, and clepsydra clock. Analemmatic sundials are sometimes designed with a human as the gnomon. The gnomon casts a broad shadow; the shadow of the style shows the time. The folding triangular gnomon is supported by a decorative open-work motif. The style is the part of the gnomon that casts the shadow. As with the gnomon, the hour-lines are all aligned with the Earth's rotational axis. The top of each column has a hole for inserting the shadow-casting gnomon, a peg. His knowledge of geometry allowed him to introduce the gnomon in Greece. Light is used to replace the shadow-edge of a gnomon.