Duration of kalA

[Sudalaimuthu Palaniappan]

Dear Indologists,
I have some questions regarding the time unit kalai (Ta.)/kalA (Skt.). and vik
alai (Ta.)/vikalA (Skt.). Tamil lexicon and MMW define these terms as given
below.


Tamil Lexicon gives the following
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kalai
...5. indian hour =1/60 of a 1/30 of a zodiacal sign; 6. a time measure;

vikalai
1. the Indian hour of 24 minutes; 2. second of a degree=1/60 kalai


MMW gives the following
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kalA
-------
f. (etym. doubtful) a small part of anything , any single part or portion of
a whole , esp. a sixteenth part RV. viii , 47 , 17 TS. ZBr. Mn. &c. ; a digit
or one-sixteenth of the moon's diameter Hit. KathAs. ... ; a symbolical
expression for the number sixteen Hcat.; ...a division of time (said to be
1/900 of a day or 1.6 minutes Mn. i , 64 Hariv. ; or 1/1800 of a day or 0.8
minutes Comm. on VP. ; or 2 minutes and 26 and  54/201 seconds Suzr. ; or 1
minute and 35 and 205/301 seconds , or 8 seconds BhavP.) ; the sixtieth part
of one-thirtieth of a zodiacal sign , a minute of a degree sUryas....

vikalA - the 60th part of a kalA, the second of a degree, sUryas.

Is the Indian hour (24 minutes) or nADikA or ghaTikA ever defined in Sanskrit
texts as 1/60 of a 1/30 of a zodiacal sign? We know kalA is used to denote
the phases of the moon as well. Why is there such a wide variation in the
duration of kalA as defined by different texts? What is the currently
accepted etymology, if any, for this word, kalA? (I am aware of Gonda's
discussion in "Old Indian", p. 195.) Similar to nADi or ghaTi, has the term
"kalaza' ever been used to describe an hour or a water-clock?

Thanks in advance.

Regards
S. Palaniappan