New light on the function of the oldest known analogue computer, the Antikythera mechanism, has been cast by researchers at the University of Glasgow.

The researchers used statistical modelling techniques, developed to analyse gravitational waves, to establish the likely number of holes in one of the broken rings of the Antikythera mechanism—an ancient artefact showcased in the recent Indiana Jones and the Dial of Destiny film.

While the movie version helped the intrepid archaeologist to travel through time, the Glasgow team’s results provide fresh evidence that one of the components of the Antikythera mechanism was most likely used to track the Greek lunar year.

The mechanism was discovered in 1901 by divers exploring a sunken shipwreck near the Aegean island of Antikythera. Though the shoebox-sized mechanism had broken into fragments and eroded, it quickly became clear that it contained a complex series of gears which were unusually intricately tooled.

Decades of subsequent research and analysis have established that the mechanism dates from the second century BCE, and functioned as a kind of hand-operated mechanical computer.

Exterior dials connected to the internal gears allowed users to predict eclipses, and calculate the astronomical positions of planets on any given date with an accuracy unparalleled by any other known contemporary device.

In 2020, new X-ray images of one of the mechanism’s rings, known as the calendar ring, revealed fresh details of regularly-spaced holes that sit beneath the ring.

Since the ring was broken and incomplete, however, it wasn’t clear just how many holes there were originally. Initial analysis by Antikythera researcher Chris Budiselic and colleagues suggested it was likely somewhere between 347 and 367.

Now, in a new paper published in the Horological Journal, the Glasgow researchers describe how they used two statistical analysis techniques to reveal new details about the calendar ring.

They show that the ring is vastly more likely to have had 354 holes, corresponding to the lunar calendar, than 365 holes, which would have followed the Egyptian calendar. The analysis also shows that 354 holes is hundreds of times more probable than a 360-hole ring, which previous research had suggested as a possible count.

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Dr Joseph Bayley, a co-author of the paper, is a research associate at the School of Physics & Astronomy. He said: “Previous studies had suggested that the calendar ring was likely to have tracked the lunar calendar, but the dual techniques we’ve applied in this piece of work greatly increase the likelihood that this was the case.

“It’s given me a new appreciation for the Antikythera mechanism and the work and care that Greek craftspeople put into making it – the precision of the holes’ positioning would have required highly accurate measurement techniques and an incredibly steady hand to punch them.

Professor Graham Woan, a fellow co-author and also of the School of Physics & Astronomy, added: “It’s a neat symmetry that we’ve adapted techniques we use to study the universe today to understand more about a mechanism that helped people keep track of the heavens nearly two millennia ago.

“We hope that our findings about the Antikythera mechanism, although less supernaturally spectacular than those made by Indiana Jones, will help deepen our understanding of how this remarkable device was made and used by the Greeks.”