Yuga-Vibhāga and Kāla-Pramāṇa
Measures of Time and the Four Yugas
चत्वार्याहुः सहस्राणि वर्षाणां च कृत युगम् / तस्य तावच्छती संध्या संध्यांशः संध्याया समः
catvāryāhuḥ sahasrāṇi varṣāṇāṃ ca kṛta yugam / tasya tāvacchatī saṃdhyā saṃdhyāṃśaḥ saṃdhyāyā samaḥ
Krita Yuga is said to be four thousand years; its twilight (saṃdhyā) is a hundred years, and its twilight-portion (saṃdhyāṃśa) is equal to that twilight.