Manasara 30.91

30.91

taccheṣaṃ cāpi nakṣatraṃ gaṇayedaśvinīkrimāt
ṣaḍaṣṭanandavṛddhyā tu saptabhiḥ kṣapayettataḥ

That remainder is the lunar asterism, which one should count in order beginning from Aśvinī; / With an increase by six, eight, or nine, one should then divide by seven;