as Maitreya told Vidura.

• All matter is an assembly of Parama anus. (Fundamental particles – atoms?). The time of a Paramanu is related to its size.
• 2 anus make a paramanu.
• tryah (trio) make  3 renus – trasarenu.
• These tiny particles can be seen through when sunshine passes through the tiny joles of a sieve or net.
• 3 trasarenus take up the time that is remembered as Truti.
• 100 of those is a Vedha
• Thrice that is a Lava
• The duration of time of three lavas is equal to one nimeṣa,
• The combination of three nimeṣas makes one kṣaṇa,
• Five kṣaṇas combined together make one kāṣṭhā,
• Fifteen kāṣṭhās make one laghu.
• Fifteen laghus make one nāḍikā,
• Two nadikas make one muhūrta,
• 6 or 7 Praharas make a Yaamaah.
• There are 4 yaamaah in the day and 4 yaamaah in the night of mortals.
• 15 days make the krshna paksha and 15 days make the sukla paksha.
• Two pakshas make a masa which makes a day and night of the Pitrs.
• 2 masas make a rtu.
• 6 such masas (months) make an ayanam – the Uttarayanam and the Dakshinanayanam the Divi (Sky – heaven)
• An ayanam is a day of the Devas.
• 12 masas is a vatsara.
• A human lives for a 100 years.
• The names of the vatsaras are Samvatsara, parivatsara, idavatsra, anuvatsra and vatsara.
• 12 divine years (varshas) form the caturyugas of krta, tretha, dvapara and kali.
• Multiplying by 4,3,2,1 in Krta etc Yugas, numbering thousands and 2 hundreds. (He is asking Vidura to multiply 1200 by 4,3,2,1, etc to get the duration of the different yugas as confirmed by Markandeya in the Mahabharata).
• The yuga sandhya periods are in hundreds of years (not in thousands in the same ratio. Matches with Markandeya)
• 1000 of the caturyugas of the trilokas, form the day of the Brahma and he has a night of equal period.
• There are 14 manus in a day of Brahma.
• Each Manu lasts a little over 71 Mahayugas.
• A 100 years of Brahma is less than a nimisha of Sri Vishnu.

Time Measuring Instrument and Method:

A copper pot weighing six palas has a hole bored in it by a gold probe weighing 4 masas, measuring 4 angulas.The time it takes to fill up with water is a called a prastha.

Courtesy : - http://oldthoughts.wordpress.com