If you try to construct a calendar involving the cycles of both moon and sun you will be in trouble. There is no way to combine their cycles within a year. But if you pass beyond a year the trick can be done.

7 * 60 = 14 * 30 = 420 = 15 * 28

 

28 is the number which rongorongo writers have chosen as a good (even) number for the number of nights in a month - the nights when the moon is visible (i.e. 'seen' by the sun).

 

420 implies the 'conjunction' of sun and moon (in a way similar to 28).

 

14 is half 28 and there are 4 weeks in a 28-night month. 4, 7, 14 and 28 therefore belong together and they point at both the moon and the sun. Similarly 6, 15, 30 and 60 point at the sun and the moon.

 

Miraculously, it seems, 14 (moon) * 30 (sun) = 420 (sun + moon) = 15 (sun) * 28 (moon).