The above item was found back in 1902 on a Roman cargo ship that had wrecked off the Greek island of Antikythera, between Kythera and Crete, and has been dated to about 150-100 BC. The Antikythera mechanism (Greek: O μηχανισμός των Αντικυθήρων transliterated as O mēchanismós tōn Antikythērōn) as it is known has always been thought to be an analog computer that was probably used to make astronomical calculations using gears like clockworks. Until recently the X-Ray machines used to see inside the device has only been able to find about 30 gears so making a working replica has been impossible. Now Michael Edmunds, a physicist at the University of Cardiff in Wales, has used a machine similar to a CT scan to see more.

According to an LA Times article:

They concluded that the device contained 37 gears, about 30 of which still survive. It was originally housed in a wooden case slightly smaller than a shoebox.

Two dials on the front show the zodiac and a calendar of the days of the year that can be adjusted for leap years. Metal pointers show the positions in the zodiac of the sun, moon and five planets known in antiquity. Two spiral dials on the back show the cycles of the moon and predict eclipses.

The complicated meshing of the gears is a physical representation of the so-called Callippic and saros astronomical cycles. In the Callippic cycle, for example, the sun, moon and Earth return to the same relative orientations four times in 76 years minus one day.

The saros cycle predicts that, following a solar or lunar eclipse, a similar eclipse will occur 223 lunar months later.

By turning the gears with a hand crank, the user could select a specific day in the past or future and observe the positions of the heavenly objects on that day.

The device was most likely used to indicate the beginning and end of growing seasons, to mark religious holidays and to time other significant events during the year.

“The design is beautiful; the astronomy is exactly right,” Edmunds said. “The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely well.”

The device performs subtractions, multiplications and divisions to carry out its functions. That leads to the question “of whether they could have easily designed actual calculators for other purposes,” Edmunds said.