Natyashastra
यथाक्षरेणैव भवेदयनोरुपवर्तनम् । उपोहनं तु वस्त्वर्धं द्विकलं प्रत्युपोहनम् ॥ २४५॥
The Upavartana should be done according to the same syllable. The Upohana is half of the Vastu, and the Pratyupohana consists of two Kalās.
english translation
yathAkSareNaiva bhavedayanorupavartanam । upohanaM tu vastvardhaM dvikalaM pratyupohanam ॥ 245॥
hk transliteration by Sanscript