An abacus is a form of manually operated counting aid that has been around for thousands of years. Abaci continue to be used in parts of Asia and Middle East, especially in shops, and they can often be acquired in stores which stock Chinese or Japanese goods. In the West, it is sometimes used as a teaching tool to help young children grasp numbers, and some mathematicians enjoy experimenting with the abacus to work out simple problems.
The design of an abacus varies, depending on the region of the world it is from, but generally it consists of a frame that supports rods or wires. The rods hold beads that can be moved around on the frame to represent various numbers. In some cases, an abacus has a crossbeam that divides the rods; the beads above the beam are multiples of five, while those below are multiples of one. Each rod represents a decimal place.
The name comes from the Greek abax, which means “counting board.” The Greeks used boards covered in sand to draw out equations as they worked on them, and they probably picked up the habit from the Hebrews, who used the word abaq to describe a counting board. Both the Greeks and Romans used various forms of the abacus; the Romans favored boards with grooves and beads or rocks, for example. The counting frame style with rods and beads appears to have originated in China.
A skilled abacist can compute a variety of basic mathematical functions on an abacus. Addition and subtraction are obviously relatively straightforward, but the tool can also be used to divide and multiply numbers, and to find square or cube roots. Many visitors to Chinese shops are familiar with the clicking sounds of an abacus in use, as well as the sudden rattling which occurs when one is shaken to reset it back to zero.
Essentially, an abacus could be viewed as a visual aid for performing basic math problems, like an extension of counting on the fingers and toes. A fair amount of skill is required to use an abacus for functions like finding cube roots; it may be possible to find a manual for doing such calculations using this tool at a bookstore. In addition to finding abaci available for purchase at shops that specialize in Asian products, it is also possible to make one with the guidance of a text to help determine the style.