Warlords Beads

Last year, Virginia Walton Pilegard's The Warlord's Puzzle explained the origins of the tangram. Now, detailing a boy's attempts to count the warlord's treasure, she investigates another mathematical invention, the abacus, in The Warlord's Beads, illus. by Nicolas Debon. A historical note traces the tool to 14th-century China; instructions for making your own abacus are included. (Sept.)