It seems that a clockwork mechanism recovered in 60 metres of water from the wreck that went down in 82 BC is the only evidence of such a device in the world. The computer was described by Dr. Derek de Solla Price, an American with a grant to study the device as a box with dials on the outside and a very complex assembly of gear wheels mounted within, probably resembling a well made 18th century clock.
Doors hinged to the box served to protect the dials, and on them, as well as on all other available surfaces, there were long Greek inscriptions describing the construction and operation of the instrument.
There are at least twenty gear wheels, all made of a low tin bronze, including a very sophisticated assembly of gears that probably functioned as a differential gear system. The input was through an axle, probably rotated by hand, that turned two trains of gears and, eventually, pointers on the dials. Thus, when the main axle was turned, all the pointers turned simultaneously at various speeds. The mechanism must have worked, because it was mended twice and assumptions have been made that it was in use at the time of the wreck.
Nothing like this remarkable instrument is preserved elsewhere. Its authenticity is unquestioned but, because there is nothing comparable its true application is still unknown. The closest known similar mechanism is a thirteenth century Islamic calendar computer.
The device is on display in the National Archaeological Museum in Athens. There is a one line explanation saying something like computer from Anti-Kythera.
BASCOM Willard, Deep Water, Ancient Ships
THROCKMORTON Peter, general editor, History From The Sea