Abacus

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 electronic calculators, during the 1980s, with some ongoing attempts to revive their use. An abacus consists of a two-dimensional array of slidable beads. In their earliest designs, the beads could be loose on a flat surface or sliding in grooves.

Later the beads were made to slide on rods and built into a frame, allowing faster manipulation.

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Source: Wikipedia · Image: Wikimedia Commons · Public domain

GOLDENSPIRAL

The mathematics of beauty — Fibonacci, the golden ratio, and the patterns that shape nature, art, and design.

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