abacus

One of the earliest counting instruments. Similar devices predate the Greek and Roman days. It uses sliding beads in columns that are divided in two by a center bar. The top is “heaven,” where each of two beads is worth 5 when moved to the center bar. The bottom is “earth,” where each of five beads is worth 1 when moved toward the center.

abacus
Bàn tính cổ xưa.