Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · Signs, Planets, Birth
जातकम् १
स्वोच्चत्रिकोणगेहा प्रनवांशैस्थानजं बलम् ।दिक्षु सौम्येज्ययोः सूर्यारयोः सौरे सिताब्जयोः ॥ २८ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 55, verse 28.
A planet gets strength of place in its own high sign and its mulatrikona (a planet's strong own-sign part) sign. It also gets it in its own sign and its own navamsha (one-ninth part of a sign). Strength of direction goes in turn to Mercury and Jupiter, the Sun and Mars, Saturn, and Venus and the Moon.
Simple meaning: A planet is strong in its high sign, own sign and own navamsha. It also gets strength from a direction.
निशींदुकुजसौराश्च सर्वदा क्षोह्नि चापरे ।
Moon, Mars and Saturn are strong at night. The rest are strong by day. Bad planets gain in the dark half.
सौरारज्ञेज्यशुक्रेंदुसूर्याधिक्यं परस्परम् ।
The planets go up in strength from Saturn to the Sun. Good planets count when they stand in a corner house.
क्लीबे तदूशनाद्वापि चंद्रार्कांशसमं जनुः ।
Bad planets in their own navamsha, good ones in others', and an animal-sign lagna point to a non-human birth.