One of the oldest manipulatives you're probably familiar with is the **abacus**, the ancient counting device in which beads strung on wires are used to represent single digits and groups of numbers.

In 2002 Fossil launched the **ABACUS** line, with technological products like Person Digital Assistants (PDAs) that are worn on the wrist like watches.

Fossil also offers a miniature PDA worn on the wrist, called **Abacus** Wrist PDA, the first company to do so.

2) closely resembles the Roman **abacus** in its construction and use.

In his large study, the walls of which were hung to the ceiling with Persian rugs, bearskins, and weapons, sat Dolokhov in a traveling cloak and high boots, at an open desk on which lay an **abacus** and some bundles of paper money.

He wrote also treatises on the astrolabe (a copy of this is in the British Museum), on the **abacus** (three copies exist in the Vatican library, the library of Leiden University and the Bibliotheque Nationale in Paris), translations of the Kharismian Tables and an Arabic Introduction to Astronomy.

The name of " **abacus** " is also given, in logic, to an instrument, often called the " logical machine," analogous to the mathematical **abacus**.

In the **abacus** the combinations are inscribed each on a single slip of wood or similar substance, which is moved by a key; incompatible combinations can thus be mechanically removed at will, in accordance with any given series of premises.

Though convenient for exhibiting the composition of any particular number, it was inconvenient for purposes of calculation; and in fact calculation was entirely (or almost entirely) performed by means of the **abacus**.