Abacus - Wikipedia
https://en.wikipedia.org/wiki/Abacus
WEBAn abacus (pl.: abaci or abacuses), also called a counting frame, is a hand-operated calculating tool which was used from ancient times in the ancient Near East, Europe, China, and Russia, until the adoption of the Hindu-Arabic numeral system. An abacus consists of a two-dimensional array of slidable beads (or similar objects). In their ...
DA: 99 PA: 89 MOZ Rank: 26