Brihat Parashara Hora Shastra
राश्याद्यं लग्नराश्यादौ योज्यं द्वादशशेषितम् । तदारभ्य क्रमादोजे दशा ज्ञेयोत्क्रमात् समे ॥ १८९॥
The Rāśi, degree etc. so available may be added to the longitude of Lagn. From the Rāśi, becoming available by doing so, will start the Dashas of the 12 Rāśis. (If that Rāśi is odd, the counting will be onwards. It will be in the reverse order, if the Rāśi is even)
english translation
rAzyAdyaM lagnarAzyAdau yojyaM dvAdazazeSitam । tadArabhya kramAdoje dazA jJeyotkramAt same ॥ 189॥
hk transliteration by Sanscript