Abacus

From Conservapedia

The abacus (pl. abacuses or abaci) was a digital calculation tool that was used to perform mathematical calculation especially for accountancy in medieval times. It works by having numbers represented by beads sliding on a rod. With it, the user can add, subtract, multiply, divide, and extract square roots. Today even though it is obsolete it is still widely used in Asia, particularly in the People's Republic of China and the Republic of China.