Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 8 · Marriage
विवाहः
ततो बलवती होरा द्रेष्काणो बलवांस्ततः ।ततो नवांशो बलवान्द्वादशांशो बली ततः ॥ ४३१ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 431.
Then the hora (half of a sign) is strong. The drekkana (one-third part of a sign) is stronger than that. Then the navamsha (one-ninth part of a sign) is strong. After it, the dvadashamsha (one-twelfth part of a sign) is strong.
Simple meaning: The finer parts of the sign grow stronger in turn: hora, drekkana, navamsha, then dvadashamsha.
त्रिंशांशो बलवांस्तस्माद्वीक्ष्यमेतद्बलाबलम् ।
The thirtieth part is strongest. All signs are good for marriage if good planets join or see them.
चंद्रार्केज्यादयः पच यस्य राशेस्तु खेचराः ।
A lagna is good when the Moon, Sun, Jupiter and the others help it.
जामित्रशुद्ध्यैकविंशन्महादोषविवर्जितम् ।
Pick a lagna free of 21 great faults and with a pure 7th house.