Skandapurana 16.105.34

16.105.34

tasmācca dviguṇaṃ jñeyaṃ nimiṣāṃtaṃ varānane ..
nimiṣaiḥ pañcadaśabhiḥ kāṣṭhā ityucyate budhaiḥ..
triṃśadbhiścaiva kāṣṭhābhiḥ kalā proktā manīṣibhiḥ ..34..

Twice that should be known as a nimiṣa, O fair-faced one;
fifteen nimiṣas are called a kāṣṭhā by the wise;
and thirty kāṣṭhās are declared to be a kalā by the intelligent.