Parts of a portable sundial-calendar, Byzantine, c 520 AD.
© Science Museum / Science & Society Picture Library
These fragments are the remains of a portable sundial with calendrical gearing. The gear wheels are the second oldest surviving examples. They are important evidence linking the earliest known geared mechanism, a Greek calendrical instrument (1st century BC), with the earliest gearing from the Islamic world, (c 1000 AD), indicating the path of transmision of this technology. The outer scale names major Greek towns with their latitudes, and these would have been used to set the instrument.