Manava Dharmashastra 1.64

1.64

sthitipralayakālaparimāṇanirūpaṇārthaṃ jyotiḥśāstragocaraṃ kālavibhāgaṃ vaktumupakramate | aṣṭādaśa nimeṣāḥ kāṣṭhā nāma kālo bhavati | triṃśatkāṣṭhāḥ kalā | triṃśatkalā eko muhūrtaḥ syāt | tāvataḥ triṃśadityarthaḥ | triṃśanmuhūrtaḥ ahorātram | vidyāditi kriyāpadamāhṛtya tāvataiti dvitīyābahuvacanam | atha ko'yaṃ nimeṣo nāma | akṣikṣmaṇornaisargikakampa unmeṣasahacārī | anyaistu paṭhitaṃ yāvatā kālena vyaktamakṣaramuccāryate sa nimeṣaḥ |

Ten and eight ‘nimeṣas’ (should be known as) one ‘Kāṣṭhā’; thirty such (Kāṣṭhās) one ‘Kalā’; thirty ‘Kalās’ one ‘muhūrta’; and as many ‘muhūrtas’ one ‘Ahorātra’ (Day and Night).—(64)

Medhātithi’s commentary (manubhāṣya):
The author now begins to describe the measures of time, which are taught in the Science of Astronomy, for the purpose of determining the exact duration of time of the continuance of the world and its dissolution.

Eighteen ‘nimeṣas’ go to make that measure of time which is known as ‘Kāṣṭhā’;—thirty ‘Kāṣṭhās’ make one ‘Kalā’;—thirty ‘Kalās’ make one ‘Muhūrta,’ and ‘as many’—i.e., thirty;—thirty ‘muhurtas’ make one ‘Ahorātra’ (Day and Night).

‘Should be known as’—this verb has got to be supplied.

‘Tāvataḥ,’ ‘a s many,’ is the Accusative Plural form.

“What is it that is called Nimeṣa?”

‘Nimeṣa is the natural winking of the Eye-lashes, which accompanies every opening of the eye. Other people have declared that ‘Nimeṣa’ is that time which is taken in the distinct utterance of one letter-sound.—(64)