 The octaeteris, a cycle of 8 lunar years popularised by Cleostratus (and also commonly attributed to Eudoxus) which was used in some early Greek calendars, notably in Athens, is 1.53 days longer than eight Julian years.The length of nineteen years in the cycle of Meton was 6,940 days, six hours longer than the mean Julian year.The mean Julian year was the basis of the 76-year cycle devised by Callippus (a student under Eudoxus) to improve the Metonic cycle.