Abacus
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An abacus, also called a counting frame, is a hand-operated calculating tool which was used from ancient times, in the ancient Near East, Europe, China, and Russia, until largely replaced by handheld
An early photograph of the Salamis Tablet.
Copy of a Roman abacus
Use of an abacus, as illustrated in Margarita philosophica (1503)
Russian schoty
Roman abacus
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The Roman hand abacus was one of the earliest known portable calculating devices, used in the Roman world. It was a base-10 form of the abacus, with movable beads held in slots rather than loose count
Abacus
…four or five beads) representing ones. Natural numbers are normally used, but some allow simple fractional components (e.g. 1⁄2, 1⁄4, and 1⁄12 in Roman abacus), and a decimal point can be imagined for fixed-point arithmetic. Any particular abacus design supports multiple methods to perform calculations…
Velser's reconstruction of Roman abacus (ca. 1600)
Representable fractions of an uncia under each interpretation