The machine was a 365-day calendar, which ingeniously factored in the leap year every four years. And it not only provided the Metonic cycle, which was known to the Babylonians, it also gave the so-called Callippic cycle, which is four Metonic cycles minus one day and reconciles the solar year with the lunar calendar.
It could also predict lunar and solar eclipses under the Saros cycle, a 223-month repetitive interplay of the Sun, Earth and Moon. This function, presumably, would been useful for religious purposes, given that eclipses are traditionally taken as omens.
The Machine was also a star almanac, showing the times when the major stars and constellations of the Greek zodiac would rise or set and, speculatively, may also have shown the positions of the planets.
But even more impressive is a tiny pin-and-slot device that factors in a movement of the Moon that, for centuries, puzzled sky-watchers. In this so-called main lunar anomaly, the Moon appears to move across the heavens at different speeds at different times - the reason being its elliptical orbit around Earth.
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