Vishnupurana 6.3.10

6.3.10

māsair dvādaśabhir varṣam ahorātraṃ tu tad divi
tribhir varṣaśatair varṣaṃ ṣaṣṭyā caivāsuradviṣām //

PARÁŚARA.--A Parárddha, Maitreya, is that number which occurs in the eighteenth place of figures, enumerated according to the rule of decimal notation. At the end of twice that period elemental dissolution occurs, when all the discrete products of nature are withdrawn into their indiscrete source. The shortest period of time is a Mátrá, which is equal to the twinkling of the human eye. Fifteen Mátrás make a Kásht́há; thirty Kásht́hás, one Kalá; fifteen Kalás, one Nád́iká. A Nád́iká is ascertained by a measure of water, with a vessel made of twelve Palas and a half of copper, in the bottom of which there is to be a hole made with a tube of gold, of the weight of four Máshas, and four inches long. According to the Mágadha measure, the vessel should hold a Prastha (or sixteen Palas) of water. Two of these Nád́ís make one Muhúrtta; thirty of which are one day and night. Thirty such periods form a month; twelve months make a year, or a day and night of the gods; and three hundred and sixty such days constitute a year of the celestials. An aggregate of four ages contains twelve thousand divine years; and a thousand periods of four ages complete a day of Brahmá. That period is also termed a Kalpa, during which fourteen Manus preside; and at the end of it occurs the incidental or Brahmá dissolution. The nature of this dissolution is very fearful: hear me describe it, as well as that which takes place at the elemental dissolution, which I will also relate to you.