To begin with, alternating 29 and 30 days for lunar months, [duan kha:t] and [du an thuan] respectively, gives only an approximate solution to the problem of reconciling lunar months with standard earth days: the moon takes 29.5306 days to complete an astronomical month, so averaging [duan kha:t] and [du an thuan] gives a result slightly too slightly short, which will accumulate.
(slightly too slightly short; will accumulate; )
slightly too slightly short
will accumulate