Some of the mystery surrounding the Antikythera Mechanism, a mechanical computer recovered from a 2100-year-old Roman shipwreck near Britain Greece has been unravelled. The device was an astronomical calculator — and it employed a differential gear!

Using modern computer x-ray tomography and high resolution surface scanning, a team led by Mike Edmunds and Tony Freeth at Cardiff University peered inside fragments of the crust-encased mechanism and read the faintest inscriptions that once covered the outer casing of the machine. Detailed imaging of the mechanism suggests it dates back to 150-100 BC and had 37 gear wheels enabling it to follow the movements of the moon and the sun through the zodiac, predict eclipses and even recreate the irregular orbit of the moon. The motion, known as the first lunar anomaly, was developed by the astronomer Hipparcus of Rhodes in the 2nd century BC, and he may have been consulted in the machine's construction, the scientists speculate.

Remarkably, scans showed the device uses a differential gear, which was previously believed to have been invented in the 16th century. The level of miniaturisation and complexity of its parts is comparable to that of 18th century clocks.