The craftsman polishes this jade with an emery wheel.
Tips
culture
The 秤砣 is the sliding weight that gives the traditional Chinese 杆秤 (hand-held steelyard balance) its precision; markets used these well into the 20th century. Hence the saying 秤砣虽小压千斤 "a steelyard weight is small but balances a thousand jin" = "small but mighty".
memory
砣 = 石 "stone" (radical) + 它 (tā, phonetic). The radical pins down "something heavy and stone-like"; the phonetic shifts from tā to tuó (a common shift for the 它 phonetic series, e.g. 驼 "camel"). All real-world uses come back to a heavy round object: balance weight, road roller, grinding wheel.
Stone radical on the left, the indexing radical. A 砣 is the heavy sliding stone weight on a steelyard balance, or a stone roller used to crush grain; both objects are literally stones, so the radical does straightforward semantic work here.
Right side 它 supplies the tā sound, which shifted to tuó in 砣's reading. The "it" meaning isn't loaded here; treat it as a pure phonetic. Same tuó/tā cluster shows up in 驼 camel and 鸵 ostrich, all bearing this graphic root.
