Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · Signs, Planets, Birth
जातकम् १
षड्वर्गार्द्धस्य त्रिंशस्य त्रिकोणगश्च स्मरगः ।सप्तमासस्य तूर्यस्य चतुरस्रगतस्य च ॥ १३८ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 55, verse 138.
A planet with the dasha (planet period) lord takes half. One in a trikona (luck house) takes a third. One in the 7th takes a seventh. One in the 4th or 8th takes a quarter. (Our text is unclear here: the first word, read as 'with the lord'.)
Simple meaning: 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.
दशागुणैर्हता भक्त्या गुणैक्येन समागताः ।
Periods are multiplied by their multipliers and divided to give years and months.