This fragment is from the remains of a portable sundial with calendrical gearing. The gear wheels are the second oldest surviving examples. They provide important evidence linking the earliest known geared mechanism, a Hellenistic calendrical instrument (dated to the 1st century BC), with the earliest gearing from the Islamic world (dated to c 1000 AD), thereby 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.
© Science Museum / Science & Society Picture Library