Brihat Parashara Hora Shastra
वर्ष द्वादशकं तत्र न चेदेकादि चिन्तयेत् । एकः स्वक्षेत्रयोऽन्यस्तु परत्र यदि संस्थितः ॥ १५९॥
their Dasha will be of 12 years. Otherwise the Dasha will be of the number of years, indicated by the number, counted from that Rāśi to the Rāśi, occupied by its Lord.
english translation
varSa dvAdazakaM tatra na cedekAdi cintayet । ekaH svakSetrayo'nyastu paratra yadi saMsthitaH ॥ 159॥
hk transliteration by Sanscript