The Callippic cycle (or Calippic) is a particular approximate common multiple of the tropical year and the synodic month, proposed by Callippus in 330 BC.
A century before Callippus, Meton had described a cycle in which 19 years equals 235 lunations, and judged it to be 6,940 days.
[1] The cycle's error has been computed as one full day in 553 years, or 4.95 parts per million.
[2] The first year of the first Callippic cycle began at the summer solstice of 330 BC (28 June in the proleptic Julian calendar), and was subsequently used by later astronomers.
In Ptolemy's Almagest, for example, he cites (Almagest VII 3, H25) observations by Timocharis during the 47th year of the first Callippic cycle (283 BC), when on the eighth of Anthesterion, the Pleiades star cluster was occulted by the Moon.