In 1950, while excavating an Upper Paleolithic fishing village in the Democratic Republic of Congo, archaeologists discovered a 20,000-year-old bone with a pattern of lines carved into it. If the lines are tally marks, as researchers suspect, then the bone would be the oldest known device used by humans to aid in mathematical calculation.

First recorded in Mesopotamia four or five thousand years ago, the abacus was used by merchants and bureaucrats to perform calculations in many ancient cultures, from Greek and Chinese to Aztec. Its columns of beads are an early form of positional notation, in which digits represent different quantities depending on where they appear in a number.