Brihat Parashara Hora Shastra
इष्टघट्यादिकं द्विघ्नं पञ्चाप्तं भादिकं च यत्। योज्यमौदयिके भानौ होरालग्नं स्फुटं हि तत्॥ ५॥
Divide the time past up to birth from sunrise by 2½ and add the quotient etc. in Rāśis, degrees and so on to the longitude of Sūrya, as at the sunrise. This will yield Hora Lagn in Rāśi, degrees etc.
english translation
iSTaghaTyAdikaM dvighnaM paJcAptaM bhAdikaM ca yat। yojyamaudayike bhAnau horAlagnaM sphuTaM hi tat॥ 5॥
hk transliteration by Sanscript