SB 3.11.6

त्रसरेणुत्रिकं भुङ्क्ते यः कालः स त्रुटिः स्मृतः ।
शतभागस्तु वेधः स्यात्तैस्त्रिभिस्तु लवः स्मृतः ॥६॥

trasareṇu-trikaṁ bhuṅkte
yaḥ kālaḥ sa truṭiḥ smṛtaḥ
śata-bhāgas tu vedhaḥ syāt
tais tribhis tu lavaḥ smṛtaḥ

trasareṇu-trikam—combination of three hexatoms; bhuṅkte—as they take time to integrate; yaḥ—that which; kālaḥ—duration of time; saḥ—that; truṭiḥ—by the name truṭi; smṛtaḥ—is called; śata-bhāgaḥ—one hundred truṭis; tu—but; vedhaḥ—called a vedha; syāt—it so happens; taiḥ—by them; tribhiḥ—three times; tu—but; lavaḥ—lava; smṛtaḥ—so called.

The time duration needed for the integration of three trasareṇus is called a truṭi, and one hundred truṭis make one vedha. Three vedhas make one lava.

It is calculated that if a second is divided into 1687.5 parts, each part is the duration of a truṭi, which is the time occupied in the integration of eighteen atomic particles. Such a combination of atoms into different bodies creates the calculation of material time. The sun is the central point for calculating all different durations.