Brihat Parashara Hora Shastra
एकादशस्य तद्दृष्टराशीनां स्थिरवत् समाः । प्रवृत्ता दृग् वशाद्यस्माद् दृग्दशेयं ततः स्मृता ॥ १८६॥
As this system is mostly based on Drishtis, it has been named, as Dirga Dasha. Three different processes are adopted for the Movable, Fixed and Dual Rāśis from Dharm, Karm and Labh. According to them, Rāśi, which receives a Drishti from the Movable Rāśi, is counted backwards and the Rāśi, receiving a Drishti from the Fixed Rāśi, is counted onwards.
english translation
ekAdazasya taddRSTarAzInAM sthiravat samAH । pravRttA dRg vazAdyasmAd dRgdazeyaM tataH smRtA ॥ 186॥
hk transliteration by Sanscript