कालिङ्गकस्तापीपाषाणो वा मुद्गवर्णो निकषः श्रेष्ठः ॥ कZ_०२.१३.२१ ॥
kāliṅgakas tāpīpāṣāṇo vā mudgavarṇo nikaṣaḥ śreṣṭhaḥ
A Kāliṅga-type stone or a Tāpi-stone—mung-bean coloured—is the best touchstone.
To standardize equipment across officials and marketplaces so results are comparable and legally defensible.