Śaiśirīya Śikṣā 87

87

śeṣāstu svaritā jñeyāḥ ṣaḍjamadhyamapañcamāḥ
udāttamākhyāti vṛṣo'ṅgulīnāṃ pradeśinīmūlaniṣṭamūrdhā

the rest are to be known as circumflex: ṣaḍja, madhyama, and pañcama; / the thumb indicates the acute, resting at the base of the forefinger;