Narapatijayacarya 3.1.3.4

3.1.3.4

prabhavādyabdamekaikamudayastvasvarādikaḥ ||
dvādaśābdasya varṣonā tadbhuktirvārṣike svare ||

For each single year beginning with Prabhava, there is indeed the rising of sounds beginning with "a"; / the sub-period of the twelve-year period, minus the year, is its experience in the annual sound.