Brihat Jataka
एकर्क्षगोऽर्द्धंमपहृत्य ददाति तु स्वं त्र्यंशं त्रिकोणगृहग: स्मरग: स्वरांशम् ॥ पादं फलस्य चतुरस्त्रगत: सहोरास्त्वेवं परस्परगता: परिपाचयन्ति ॥ ८-३ ॥
A planet located with the dasa lord takes half of the period of dasa lord and shows it as its sub-period, a planet in 5th or 9th from the dasa lord has 1I3rd of the period of dasa as its sub period. A planet 7th from the dasa lord has 1I7th of the period of the dasa lord as its sub-period. A planet in 4th or 8th from the dasa lord has 1/4th of the dasa lord's period as its sub-period. Thus planets including the lagna have their subperiods. ln case there are more than one planets in a house, the strongest of themail alone will have its sub-period, The order of the sub-periods will be - first the dasa lord, then the one with it, next 7th one in 5th or 9th from it, then the one in 7th from it and last of all the planet in 4th or 8th from the dasa lord.
english translation
ekarkSago'rddhaMmapahRtya dadAti tu svaM tryaMzaM trikoNagRhaga: smaraga: svarAMzam ॥ pAdaM phalasya caturastragata: sahorAstvevaM parasparagatA: paripAcayanti ॥ 8-3 ॥
hk transliteration by Sanscript