Brihat Parashara Hora Shastra
उच्चखेटस्य सद्भावे वर्षमेकं च निक्षिपेत् । तथैव नीचखेटस्य वर्षमेकं विशोधयेत् ॥ १६५॥
In addition 1 should be added in the number of years in the case of a Rāśi with an exalted Grah and 1 should be deducted from the number of years in the case of a Rāśi with a Grah in debilitation.
english translation
uccakheTasya sadbhAve varSamekaM ca nikSipet । tathaiva nIcakheTasya varSamekaM vizodhayet ॥ 165॥
hk transliteration by Sanscript