The Antikythera Mechanism

The Antikythera Mechanism; an ancient Greek gear, that's use was shrouded in mystery until decades after it was discovered (1900), is now thought to be an astronomical clock. Technology of this sort didn't resurface until 14th century Europe.

Precise, in terms of its astronomical uses, the device is simply extraordinary and is seen as the oldest scientific calculator to exist, estimated to be from around 150-100 BC. With more than 30 gears, the date would be entered via a crank and the Antikythera would calculate the position of various astronomical objects such as the planets and stars. Before such a device, astronomy was the only reference of time.