Surya Siddhanta
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तद्वद् एव विमर्दार्धनाडिकाहीनसम्युते। निमीलनोन्मीलनाख्ये भवेताम् सकलग्रहे॥
In the same manner, the time of the middle of a total eclipse diminished and increased (separately) by the exact first and second mardárdhas gives the times of the beginning and end of the total darkness (respectively).
english translation
Chapter 4
Verse 16
Verse 18