Abaci pl. : of Abacus

Example:
What are the benefits of learning the abacus?

Taxonomy
abacus, beads, Nepohualtzintzin, wire, Russian abacus, Chinese abacus, suanpan, grooves, calculations, the Chinese, instrument, Greek, Roman abacus, the Roman, The Russian, bead wire, Japanese abacus, School.

Defination from the web:
abacus, also called a counting frame, is a calculating tool used primarily in parts of Asia for performing arithmetic processes. ... Around the world, abaci have been used in pre-schools and elementary schools as an aid in teaching the numeral system and arithmetic. ...