Changes
/* Description */ Apollonius of Perga
The mechanism also has a Callipic pointer. The Callipic cycle consists of four Metonic cycles and is therefore 76 years long. The Metonic cycle gives the length of a year as 365.26 days while the Callipic cycle gives 365.25 days. The correct value is 365.2422 days.
There is a gear to adjust the speed of the moon pointer depending on the time of month. This follows the lunar epicycle theory of Apollonius of Perga. In modern terms, this the variation reflects the fact that the moon's orbit is somewhat elliptical rather than perfectly circular.
==References==
