Kautilya's Arthashastra 2.20.39

2.20.39

chāyāyām aṣṭapauruṣyām aṣṭādaśabhāgaś chedaḥ, ṣaṭpauruṣyāṃ caturdaśabhāgaḥ, tripauruṣyām aṣṭabhāgaḥ, dvipauruṣyāṃ ṣaḍbhāgaḥ, pauruṣyāṃ caturbhāgaḥ, aṣṭāṅgulāyāṃ trayo daśabhāgāḥ, caturaṅgulāyāṃ trayo 'ṣṭabhāgāḥ, acchāyo madhyāhna iti //

When the length of shadow is eight paurushas (96 angulas), it is 1/18th part of the day.

When it is 6 paurushas (72 angulas), it is 1/14th part of the day; when 4 paurushas, 1/8th part; when 2 paurushas, 1/6th part; when 1 paurusha, ¼th part; when it is 8 angulas, 3/10th part (trayodasabhágah); when 4 angulas, 3/8th part; and when no shadow is cast, it is to be considered midday.