Q: Can you describe the mechanism?
A: Imagine something the size of a shoe box. … There’s a circular dial representing the zodiac signs with pointers for the position of the sun and moon. Also, probably – this part is missing, but inscriptions refer to it – two huge dials.
Q: The purpose?
A: The top one, in the form of a five-turn spiral, would track the metonic cycles over a 19-year period. It was a useful calendar for determining when the full moon would come back. The bottom dial predicted possible eclipses of the sun and moon.
Story: Allan Turner, Houston Chronicle | Photo: Wikimedia Commons