The first member of a tat-puruṣa samāsa preserves its original accent when the second member is a dvigu samāsa (Numeral Determinative Compound) denoting 'measure or quantity'.,
Thus प्रा꣡च्यसप्तसमः and गा꣡न्धारिसप्तसमः ॥ The word सप्तसमः = सप्तसमाः प्रमाणमस्य, the affix मात्रच् denoting 'measure' 5.2.37 is elided (See 5.2.37 Vartika) प्राच्यश्चासौ सप्तमश्च = प्रा꣡च्यसप्तसमः \an Eastern seven-years old\. So also गान्धा꣡रिसप्तसमः or षट्समः ॥ प्राच्य has acute on the first; while गान्धारि is either accented on the first or on the middle; as it belongs to the Kardamadi class (Phit III. 10). Why do we say 'before a Dvigu'? Observe व्रीहिप्रस्थः ॥ Why do we say 'when denoting measure?' Observe परमसप्तसमः ॥,