The affix vatup comes in the sense of 'that where of this is the measure of volume' after the words 1.yad 2. tad and 3. etad being in the Nominative 1st-Case of construction.,
Karika
डावतावर्थवैशेष्यान्निर्देशः पृथुगुच्यते ।
मात्राद्यप्रतिघाताय भावः सिद्धश्च डावतोः ॥
The phrase तदस्य is understood here. As यत् परिमाणमस्य = यावान्. This form is thus evolved; यत् + वतुप् = यावत् (the ti अत् being replaced by आ by 6.3.91 = यावन्त (the नुम् being added by 7.1.70) = यावान्त (the अ being lengthened by 6.4.41); the vibhakti सु being elided by 6.1.68, and त् being elided by 8.2.23 we get finally यावान्, तावान्, एतावान् ॥ The परिमाण is used in this sutra, in order to distinguish it from the word प्रमाण used in the last aphorism (See 5.1.19). Therefore यत्, तद् & एतद् take the affixes 'matra' &c also in the sense of प्रमाण, which would not have been the case, had परिमाण not been used in the sutra, for then the special affix वतुप् would have debarred matrach &c in the case of यत् &c. The word डावतु in the karika is the name given to this affix वतुप् by the ancient grammarians; so that according to them there was no necessity of 6.3.91 to replace टि of यत् &c, by आ; thus यत् + डावतु = यावत् ॥
Moreover the affix वतुप् being added in the sense of परिमाण, (capacity ) only after यत् &c, it follows that the words so formed, may take the further affix मात्रच् &c in the additional sense of प्रमाण (length); which would not have been the case had the word परिमाण not been used in the sutra. Thus तत् परिमाणमस्य = तावद् as धान्यं राशीकृतं । From this तावत् we have तावत् प्रमाणमस्य कुड्यादेः = तावन्मात्रम् meaning यावद् राशीकृतस्य धान्यस्य दैर्घ्ये, तादृग् अस्यापि ॥
Vart:- The affix वतुप् comes in the sense of 'like this', after the words युष्मद् and अस्मद् in the Chhandas. As त्वावतः पुरुवसो यज्ञं विप्रस्य मात्रतः ॥,