Surya Siddhanta
अप्राप्य च भवेत् पश्चाद् एवम् वापि निमीलनात्। तयोर् अन्तरनाडीभिर् हन्याद् भूपरिधिम् स्फुटम् ॥
- (but if it begins or ends) before the instant (when it begins or ends at the Middle Line, then) the given place is west of the Middle Line. Find the difference in Ghaṭikás between the times (of the beginnings or ends of the Moon's total darkness at the given place and the mid-night, which difference is called the Des'ántara Ghaṭikás.)
english translation
aprApya ca bhavet pazcAd evam vApi nimIlanAt। tayor antaranADIbhir hanyAd bhUparidhim sphuTam ॥
hk transliteration by Sanscript