Assertion: bead abacus | /r/AtLocation | the book of xu yue
Facets:
Source sentences:
text: The long and gradual improvement of the chinese counting board leaded to development (sometimes in 2nd century) of a more convenient type of abacus—the bead abacus, mentioned in the book of Xu Yue, Supplementary Notes on the Art of Figures, written about the year 190 A. D.