The affix mayaṭ (matha with feminine in ṅīp) comes when denoting a thing given in exchange in the sense of 'containing so many times more of something' or 'the price of a portion of this is so many equal portion of the other' after a Numeral.,
The word तदस्य from 5.2.36 should be read in this. The sense of the aphorism is \after a Numeral in the first case in construction (तद्), with the force of a genitive (अस्य), comes the affix मयट्, when the word in the first case in construction denotes the value (निमान) of a portion (गुण)\. The word गुण means भाग or \portion\, and निमान means 'price'. In comparing the quality of one thing with another, निमान is the value or price. Thus यवानां द्वौ भागौ निमानमस्योदश्विद्भागस्य = द्विमयमुदश्विद्यवानाम् \two parts of Yava is the price of one part Udasvit\. Similarly त्रिमयम्, चतुर्मयम्, lit. \Udasvit is द्विमय or 'two-times' the value of yava\.
The word गुणस्य is in the singular number. The comparison must therefore be made with one portion of a thing, with the several portions of the other. The ratio must be x:1, but never x:2, or x:3 &c. Therefore the rule does not apply here, द्वौ भागौ यवानां त्रय उदश्वितः ॥ The x also must be more than one. The rule therefore does not apply here: एको भागो निमानमस्य ॥
The word गुण denotes an integral number, therefore the rule will not apply to fraction. As द्वौ भागौ यवानामध्यर्द्ध उदश्वितः ॥
The affix also comes in the sense of purchasing or the comparative value of a thing, i. e. in denoting the thing received in exchange (निमेय) As उदश्वितो द्वौ भागौ निमेयमस्य यवभागस्य = द्विमयाः, as द्विमया यवा उदश्वितः = उदश्वितो द्वौ गुणौ निमेयौ येषामेकगुणानां यवानां \the exchange value of Udasvita is twice as much as that of a Yava\. The word निमान means the thing given in exchange; and निमेय the thing received in exchange. Both words are reciprocal and are terms of barter or exchange, but they do not apply to sales or purchases for coins.
Why do we say गुणस्य 'of a portion'? Observe द्वौ व्रीहियवौ निमानमस्योदश्वितः ॥ Here being no comparison of ratios, there is no affixing.
Why do we say निमाने \in denoting the thing given in exchange\? Observe, द्वौ गुणौ क्षीरस्य एकस्तैलस्य = द्विगुणं पच्यते तैलं क्षीरेण \one part of oil cooks or absorbs as much as two parts of milk\. Here the sense is that of 'cooking' and not of purchasing.
In short मयट् has the meaning of 'time or fold'. As द्विमय \two time\, the word qualifying sometime the निमान, sometime the निमेय; e.g. द्विमयमुदश्वित् यवानां 'Udasvit is two-times or two-fold of Yava in value', or द्विमया यवा उदश्वितः \two-times Yava are equal to one Udasvit\.,