Dear list members,

I've been asked to confirm the meaning of kalā in the premodern  Indian system of time units. 

 referring to the  Sūrya Siddhānta, 1 kalā = 30 kāṣṭhā approximately equal to 48 seconds but I've also been told that 1 kalā  is about one hour of the western time units. Can someone confirm the meaning of  kalā in the Indian system of time units . Was there more than one system of time units in general use in premodern India?