Siddhanta Shiromani (Crown of Treatises)

On this matter, Shripati Bhatta original: "श्रीपतिभट्टः" — A significant authority in Jyotisha (astronomy/astrology) states that for the knowledge of the origin and progression [of time]... the thirtieth part of a Blink nimeṣa is declared to be the Tatpara part.

28 It is said that eighteen Blinks nimeṣa make one Kashtha kāṣṭhā. Thirty such kashthas are called a Kala kalā. Thirty kalas make a long Ghatika ghaṭikā.

For human beings, a Nadi nāḍī Another term for a Ghatika, approximately 24 minutes consists of 360 original: "खगुणै" — kha-guṇaiḥ, a numerical code where 'kha' (space) is 0 and 'guna' (qualities) is 3, read right-to-left as 30; however, in the context of breaths and syllables, it refers to the 360 long syllables that make a unit Long Syllables gurv-akṣara. Six Breaths pala make a certain measure, and sixty of those original: "खषद्भिः" — kha-ṣadbhiḥ, meaning 60 make a Ghatika. Sixty [Ghatikas] make a full day, and thirty original: "खरामैः" — kha-rāmaiḥ, meaning 30 such days make a Month. Twelve of those months constitute a Year. This is the calculation of the divisions of Time through its own internal logic.

Specifically, the time it takes for a healthy man to blink his eye is conventionally designated by the term Nimesha. One-thirtieth part of that is known as a Tatpara. This is also confirmed in the Surya Siddhanta The foundational "Sun Treatise" of Indian astronomy:

"The time during which the eye of a healthy man flickers or blinks is called a Nimesha."

The thirtieth part of that is a Tatpara, and the hundredth part of a Tatpara is a Truti truṭi. By this, the following is explained:

1. One hundred Trutis make one Tatpara.
1. Thirty Tatparas make one Nimesha.
1. Eighteen Nimeshas make one Kashtha.
1. Thirty Kashthas make one Kala.
1. Thirty Kalas make one Nadi-Ghatika.

A Ghatika is defined as the sixtieth part of the time it takes for the entire circle of constellations to complete one rotation. This is what is meant by a "long ghatika." A pair of these units defines a Muhurta muhūrta A unit of approximately 48 minutes. Thirty such muhurtas make one Day-and-Night ahorātra. This cycle of Day-and-Night, which is the basis of our calculation of time, is perceived through the movement of the sun in its celestial path...