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Saturday, February 23, 2019

This Perpetual Calendar Hidden in an Italian Chapel Is a Mathematical Marvel | Stories - Atlas Obscura

The 19th-century device accurately tracks 4,000 years with nine cylinders and a crank, as Atlas Obscura reports.
The Perpetual Calendar tracks 4,000 years with nine rolls and a hand-operated crank.
Photo: Ranna Utida

A very early computer, quite unlike any other, is discreetly hanging in the sacristy of a small chapel in the heart of Turin, the beautiful Italian city at the foot of the Alps. Thousands of people pass by every day along Via Garibaldi, one of the main shopping thoroughfares in town, but hardly anyone knows it is there. That is because the tiny baroque jewel that owns the artifact is hidden in plain sight, and the church only opens on Saturday afternoons and Sunday mornings for mass. Still, anyone in-the-know or curious enough to find it will be awestruck by the Perpetual Calendar of Giovanni Antonio Amedeo Plana.

Built by the astronomer and mathematician in 1831, the Perpetual Calendar took 10 years to complete, from planning to assembly. The device, which resides in the Chapel of Bankers and Merchants, operates via a simple wooden crank under the adorned golden frame, a crank that hides a stunningly accurate universal mechanical calculator spanning the years 1 to 4,000. Want to know the day of the week that the Western Roman Empire fell to the barbarians, on September 4, 476? The calendar will tell you that it was a Monday. Or maybe the phase of the moon on the day you were born? Or the date of Easter a thousand years from now (April 18, 3019)? All of this information can be accessed by a pre-internet machine made of fragile wood and paper, and communicated through 46,000 little numbers carefully arranged around nine cylinders. Each of these is linked to a central one—the only adjustable part of the device—where the user can input the year. That cylinder synchronously regulates all the others through gears and chains...

Details of how the device actually works were more or less a secret until very recently. Plana, for all his assiduousness, did not leave any written material describing the mechanism inside. So in 2015 the prestigious Polytechnic University of Turin challenged its students to parse the algorithm that governs the machine. Four teams responded to the call. “This challenge has shown itself a useful way of valorizing the territory, proposing the use of engineering disciplines to improve the fruition of cultural goods,” the university’s vice dean of research, Enrico Macii, said in a statement at the time.

Source: Atlas Obscura