Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · Signs, Planets, Birth
जातकम् १
एतद्योगजमायुः स्यादथ स्पष्टमुदीर्यते ।सूर्याधिक बले पैंडं निसर्गाच्च विधोर्बले ॥ ११९ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 55, verse 119.
This is the life got from combinations. Now the exact method is told. If the Sun is strongest, use the pinda (total figure). If the Moon is strongest, use the nisarga (natural lifespan).
Simple meaning: The exact life is worked out with a method that follows the strongest of the Sun and Moon.
अंशायुः सबले लग्ने तत्साधनमथो शृणु ।
If the rising sign is strongest, the degree method is used. Full years for each planet are listed.
नखा विधुर्द्वावंकाश्च धृतिः स्वाक्षिखमार्गणाः ॥ १२१ ॥
The natural years for each planet are listed.
पिंडे निसर्गे रवोच्चे नो ग्रहः षट्भाल्पको यदा ।
A planet's full years count by how far it stands from its low point.