The back dials. Text in red is traced from X-ray CT; text in blue is reconstructed. Top, the Metonic dial is the main upper dial: a 19-year calendar with 235 months round a five-turn spiral. Top Right, the Olympiad dial is identified here for the first time. It is a four-year dial, representing the cycle of the Panhellenic Games, a central part of ancient Greek culture and a common basis for chronology. Top Left, the hypothetical Callippic dial, which follows a 76-year cycle, indicated on the back door inscriptions. Bottom, the Saros dial is the main lower dial: an 18-year (223-lunar month) scale over a four-turn spiral, for predicting eclipses. Predictions are shown in the relevant months as glyphs, which indicate lunar and solar eclipses and their predicted times of day. Within the Saros dial is shown a subsidiary dial, the Exeligmos dial: this is a 54-year triple Saros dial, whose function is to correct the glyph times in hours for successive turns of the Saros dial.
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