Matsya Purana — Characteristics of Dvāpara and Kali Yugas
चतुर्युगाणां सर्वेषाम् एतदेव प्रसाधनम् एषां चतुर्युगाणां तु गणिता ह्येकसप्ततिः //
caturyugāṇāṃ sarveṣām etadeva prasādhanam eṣāṃ caturyugāṇāṃ tu gaṇitā hyekasaptatiḥ //
This alone is the established rule for the reckoning of all the cycles of the four Yugas; and the computed number of these Caturyugas is indeed seventy-one.
It does not describe Pralaya directly; it fixes a time-reckoning rule by stating that the standard count of caturyugas (four-yuga cycles) is seventy-one, a key unit used when describing cosmic eras that frame creation and dissolution narratives.
Indirectly, it supports dharma by grounding ritual calendars, royal chronologies, and auspicious timing in an authoritative cosmic measure—useful for kings and householders who align vows, rites, and governance with sacred time.
No direct Vastu or temple rule is stated; the practical ritual takeaway is that sacred planning (festivals, consecrations, long rites) depends on correct kala-ganana, and this verse affirms the canonical count of 71 caturyugas used in broader Puranic computations.