The abacus (pl. abacuses or abaci) is a digital calculation tool that was used to perform mathematical calculation especially for accountancy in medieval times. It represents numbers with beads sliding on a rod. With it, the user can add, subtract, multiply, divide, and extract square roots. Even though it is obsolete it is still widely used in Asia, particularly in the People's Republic of China and the Republic of China, where a skilled operator can calculate as rapidly as a person using a modern electronic calculator.