Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 1 · Muhurta: Marriage, Home, Farming
ज्योतिःशास्त्रम्
हन्याल्लिप्तां गतागामिपिण्डसंख्याफलान्तरैः ।षष्ठ्याऽऽप्तं प्रथमोच्चार्ये हानौ देयं धने धनम् ॥ १८ ॥
In the full Agni Purana this is chapter 122, verse 18.
Multiply the minutes by the difference between the past and coming table figures of the pinda (total figure). Divide by sixty. In the first-named part, take it away when the figure falls. Add it when it rises.
Simple meaning: Find the in-between value: multiply the minutes by the step difference and divide by sixty.
द्वितीयोच्चरिते वर्गे वैपरीत्यमिति स्थितिः ।
In the second group the rule is reversed. Then the moon day is doubled and a sixth taken off.
रविकर्मविपरीता तिथिनाडीसमायुता ।
Apply the Sun's correction in reverse and add the moon day ghatikas. If the minus is too big, see the next verse.
सषष्टिकं प्रदेयं तत्षष्ठ्याधिक्ये च तत्त्यजेत् ।
If the minus is too big, borrow sixty. Above sixty, drop sixty. The star is found from the moon day.