Tools Of The Trade: The Abacus, NPR Article

A 'disguised scheme for compensated emancipation': Accounting for gradual abolition in nineteenth century New Jersey - Evelyn McDowell, Theresa Hammond, 2023

When were calculators first invented, and what are some of the brands made in Japan? - Quora

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Abacus, Definition, History, Origin, & Facts

Who Invented the Abacus: A Brief History - EnthuZiastic

FwA Abacus and Counting Tools History

National Museum of American History

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the abacus from ancient China; its characteristic is that the counting system used before modern numbers is still used by some businessmen, traders

Digital Standard Abacus-20 cm-Professional 13-Column Soroban Calculator (Functional and Educational Tool)

abacus - Kids, Britannica Kids

The crew of Apollo 13 used a 5-inch, metal slide rule, model N600-ES made by Pickett as a back up on-board computer. It was a model that was popular among engineers, scientists