In a dvigu samāsa (Numeral Determinative Compound) the first member preserves its original accent before a stem ending in a simple vowel with the exception of a (ik) before a word denoting time, as well as before 1. kapāla 2. bhagāla and 3. śarāva,
Thus प꣡ञ्चारत्निः, द꣡शारत्निः ॥ The above are examples of Taddhitartha Dvigu 2.1.52, equal to पंचारत्नयः प्रमाणमस्य, the प्रमाण denoting-affix मात्रच् is always elided in Dvigu (V. 2. 3 Vartika). So also प꣡ञ्चमास्य, द꣡शमास्यः = पञ्च मासान् भृतो भूतो भावी वा. This is also a Taddhitartha Dvigu 2.1.52, formed by the affix यप् 5.1.80 — 6.1.82. So also प꣡ञ्चवर्षः द꣡शवर्षः the affix ठञ् being elided (V. I. 88). So also प꣡ञ्चकपालः, द꣡शकपालः, प꣡ञ्चभगालः, द꣡शभगालः, प꣡ञ्चशरावः, द꣡शशरावः ॥ These are also Taddhitartha Dvigu formed by 4.2.16, the affix अण् being elided by 4.1.88.
Why do we say \before an इगन्त stem &c\? Observe पंचभिरश्वैः क्रीतः = पंचाश्वः꣡, दशाश्वः꣡ ॥ Why do we say \in a Dvigu Compound ?\ Observe परमारत्निः꣡, परमशराव꣡म् ॥
When these Dvigu compounds, by case-modifications do not end in इक् vowel, but the vowel is replaced by a semivowel or Guna, the rule will still apply. Thus प꣡ञ्चारत्न्यः or प꣡ञ्चारत्नयः ॥ This is done on the strength of the maxim असिद्धं बहिरङ्गमन्तरङ्गे. \That which is bahiranga is regarded as not having taken effect or as not existing, when that which is antaranga is to take effect:\ because the substitution of semivowel or guna is a bahiranga operation in relation to accent. Or the substitutes may be considered as sthanivat to the short-vowel which they replace.,