Reconstruction of a Byzantine sundial-calendar based on the remains of a portable sundial with calendrical gearing in the Science Museum's collection. The original sundial is the second oldest survivng example of a such a device with gear wheels. It provides important evidence linking the earliest known geared mechanism, a Hellenistic calendrical instrument, (1st century BC), with the earliest gearing from the Islamic world (c AD 1000), indicating the path of transmision of such technology. The outer scale names major Greek towns with their latitudes, and these would have been used to set the instrument.

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