Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 3 · Name Letters and Chakras
युद्धजयार्णवः (चक्राणि)
नैर्ऋताच्च नयेच्चन्द्रं चन्द्रादग्निं ततो जले ।जलादीशे चरेद्राहुर्विष्ट्या सह महाबलः ॥ १५ ॥
In the full Agni Purana this is chapter 142, verse 15.
From the south-west, take the line to the Moon's quarter, the north. From there go to the south-east, then to the west. From the west, go to the north-east. Rahu moves like this with vishti (bad half of a moon day). He is very strong.
Simple meaning: Rahu with Vishti goes round the directions from the south-west through the north and south-east to the west and north-east.
विष्टिराहुं प्रवक्ष्यामि अष्टौ रेखास्तु पातयेत् ।
Vishti Rahu uses eight lines moving round the directions from the north-east to the south, north-west, east and west.
ऐशान्यां च तृतीयादौ सप्तम्यादौ च याम्यके ।
Rahu sits in different directions on different moon days. In the north-west he kills enemies.
इन्द्रादीन्भैरवादींश्च ब्रह्माण्यादीन्ग्रहादिकान् ।
Groups of eight, led by Indra, Bhairava, Brahmani and the planets, go round from the east. Vatayogini starts from the south.