Matsya Purana — Measures of Time: Caturyuga Computation
प्रयुतं तु तथा पूर्णं द्वे चान्ये नियुते पुनः षण्णवतिसहस्राणि संख्यातानि च संख्यया त्रेतायुगस्य संख्यैषा मानुषेण तु संज्ञिता //
prayutaṃ tu tathā pūrṇaṃ dve cānye niyute punaḥ ṣaṇṇavatisahasrāṇi saṃkhyātāni ca saṃkhyayā tretāyugasya saṃkhyaiṣā mānuṣeṇa tu saṃjñitā //
A prayuta (ten thousand) is taken as complete; and again, two niyutas (two hundred thousand) together with ninety‑six thousand are reckoned by calculation. This is declared to be the human-number (mānuṣa-saṃjñā) for the measure of the Tretā-yuga.
It does not describe Pralaya directly; it establishes a precise numerical framework for yuga-duration, which is part of the larger Purāṇic cosmology used to situate cycles of creation and dissolution in time.
Indirectly, it provides the time-scale (yuga framework) within which dharma is said to rise and decline; kingship and household ethics in the Purāṇas are often explained as varying with the yuga, so knowing the yuga-measure supports that broader teaching.
No Vāstu or ritual procedure is stated here; the verse is a technical statement on numerical reckoning (saṅkhyā) for the Tretā-yuga, which can still inform ritual calendars and Purāṇic chronological references.