question about dholavira calendar yantra

[Anand Ganesh]

Dear Prof. RN Iyengar,

I hope you are doing well. I had a question about an astronomical contraption in Dholavira, hope you can shed some light on it. You may have seen the relevant 2013 paper by Mayank Vahia and Srikumar Menon, cited further down.

The contraption tells you the month of the year based on where a narrow beam of light illuminates a certain plank. I was wondering if you have seen references to any such yantram in shulba sutra, etc. The 'yantram' is effectively a circular room with a hole on the top that lets in a narrow beam of light. It's a peculiarly shaped room, and could have additional significance not captured by the word 'observatory' as suggested in the paper.

Reference:

Fig 14, p. 6 of: https://arxiv.org/pdf/1310.6474 

Mayank Vahia, Srikumar Menon, "A Possible Harappan Astronomical Observatory at Dholavira", Journal of Astronomical History and Heritage, 2013

Thanks, and regards,

Anand Ganesh