Cranmer abacus (14 h 39 m, 21 nov 2018 año – 1 ene 1962 año)

Descripción:

An adapted abacus, invented by Tim Cranmer, called a Cranmer abacus is still commonly used by individuals who are blind. A piece of soft fabric or rubber is placed behind the beads so that they do not move inadvertently. It placed on the market by the American Printing House for the Blind, and is still manufactured today.

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