Hayanaratna · by Balabhadra
Chapter 1 · Planets, Signs, Year Entry
ग्रहराशिस्वरूपवर्षप्रवेशाद्यानयनाधिकारः
तृतीयसन्धिरेकाढ्यस्तुर्यसंधिर्भवेदिह ॥द्व्याढ्यस्तृतीयभावोपि पुत्रभावो भवेत्स्फुटः ॥
Here the 3rd sandhi (junction between two houses) plus one sign is the 4th sandhi. And the 3rd house plus two signs is the true 5th house.
Simple meaning: 4th junction: 3rd junction plus one sign. 5th house: 3rd house plus two signs.
आढ्यो द्वितीयसंधिः स्यात्संधिः पञ्चमभावजः ॥
Houses 5 and 6: the 5th junction comes from the 2nd junction (the number of signs is not given); 6th house: 2nd house plus four signs; 6th junction…
लग्नाद्याः संधिसहिता भावाः षड्राशिसंयुताः ॥
Houses 7 to 12: add six signs to houses 1 to 6 and their junctions.
अथ केवललग्नज्ञानादेव सकलभावराशिसाधनार्थं सुगमोपायो मत्कृत
Easy method for all houses: find the rising sign's day-length difference and take it from 15 (rising sign Aries to Virgo).