तन्त्रसार (महामाहेश्वर अभिनवगुप्त - तन्त्रालोक का प्रामाणिक सार-संग्रह सटीक)

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The course along which prāṇa and apāna move, measures
thirty six digits ( anguli ). It is assumed by the Yogin that
the hour, the tithi and other long and short units of time
get their rise in prāṇa. It is to be noted here that kriyāśakti
which operates externally as kālaśakti in prāṇa, is without
any definite form. For this reason whatever shines in prāṇa
as kṣaṇa, lava etc., may shine as a year or more than several
years. Not only that, they shine and rise in it and terminate
in the highest equilibrium.
When prāṇa runs the course of two and one fourth of
a digit the duration is known as tuṭi. Four of such tuṭis
make a prahara. Half of a tuṭi is a sandhyā. The exhaling
and the inhaling represent the day and the night.
In the same way a month consisting of thirty tithis with
the broad divisions of two fortnights, is also assumed by the
Yogin to rise in prāṇa. All the tithis from pratipat to
amāvasyā and then again from pratipat to purṇimā lie along
the course of inhaling and exhaling movemsnt of prāṇa and
apāna. The sixteenth consisting of half a tuṭi at the start
and another half at the final resting place, is considered
to be the sandhyā, the meeting point of the day and the
night. These two halves of tuṭis are free from the influence
of Time, for this reason sandhyās are considered to be very
auspicious. Similarty during the dark fortnight the moon
or the apāna offers its digits ( kalā ) one by one to prāṇa,
the sun and the final one is offered near the dvādaśānta at
the fifteenth tuṭi, after which the moon gets itself dissolved
in the sun. This is known as amāvasyā when the moon
remains latent in the kalā known as amā. The span which
is one half of the tuṭi is occupied by amāvasyā and the
remaining half is the duration for pratipat. When on