《宋书·志·卷十九》
圆如舂米的碓头，上面大，下面小，如今民间还常有这一乐器。
圆如碓头，大上小下，今民间犹时有其器。
It is round like the head of a rice-pounding mortar, with a large top and a small bottom. This musical instrument is still common among the people nowadays.