Brihat Parashara Hora Shastra
मेषादित्रित्रिभैर्ज्ञेयं पदमोजपदे क्रमात् । दशाब्दानयने कार्या गणना व्युत्क्रमात् समे ॥ १५६॥
Beginning with Aries, the signs are to be understood in groups of three. For odd-footed (odd) signs, the count for determining the Daśā years is made in the regular (forward) order; for even-footed (even) signs, the count is made in the reverse order.
english translation
meSAditritribhairjJeyaM padamojapade kramAt । dazAbdAnayane kAryA gaNanA vyutkramAt same ॥ 156॥
hk transliteration by Sanscript