Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · Signs, Planets, Birth
जातकम् १
ततः केंद्रादिगानां तु द्वित्र्यादौ सबलस्य च ।बह्वायुर्यो वीर्यसाम्येर्काद्युतस्य प्राक् याचकः ॥ १३७ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 55, verse 137.
Then come those in the corner houses, and so on. Among two or three there, the strongest goes first. With equal strength, the one with more years goes first. Then the one that rose first from the Sun's light gives its period first. (Our text is unclear here: the last words, read this way.)
Simple meaning: Planet periods run in order of house, strength and years.
षड्वर्गार्द्धस्य त्रिंशस्य त्रिकोणगश्च स्मरगः ।
Planets share the sub-periods by their house from the period lord.
क्रमः केंद्रादिकोऽत्रापि द्वित्र्यादौ सबलस्य च ।
The period lord's share is 84, a planet with it 42.
त्रिकोणस्थस्य चाष्टाक्षिसूर्या द्यूनगतस्य च ।
Planets in the luck houses, the 7th, and the 4th or 8th get their own shares.