This is the principle behind the armillary sphere and the equatorial bow sundial. 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. He also wrote on mechanical devices like the astrolabe and sundial. Additionally, al-Khwarizmi wrote about the astrolabe, sundial, and elaborated on Ptolemy's geometric model. These early water clocks were calibrated with a sundial. The Quarter Mile is actually long when measured between the mobius sculpture and the sundial. Pliny referred to a solar meridian, not a sundial. The design of the circular park doubles as the face of a giant sundial. The garden is filled with plants, fountains, birds, a giant sundial, and more. The shadow of a sundial moves clockwise on latitudes north of the subsolar point. Solar time can be crudely measured by a sundial. Collections of sundial mottoes have often been published through the centuries. There is an early canonical sundial on the south wall.