Brihat Parashara Hora Shastra
सूर्यात् कुजात् सुखं जीवाज्ज्ञाच्चाऽस्तं लग्नमार्क्रितः । दशमं च भृगोश्चन्द्राद् हित्वा षड्भाधिके सति ॥ ७॥
Dig Bal. Deduct Bandhu Bhava (Nadir) from the longitudes of Sūrya and Mangal, Yuvati Bhava from that of Guru and Budh, Karm Bhava from that of Śukr and Candr and lastly Lagn from that of Śani. If the sum is above 180 degrees, deduct the sum from 360. The sum arrived in either way be divided by 3, which will be Dig Bal of the Grah.
english translation
sUryAt kujAt sukhaM jIvAjjJAccA'staM lagnamArkritaH । dazamaM ca bhRgozcandrAd hitvA SaDbhAdhike sati ॥ 7॥
hk transliteration by Sanscript