Cranmer abacus (14 ore 39 min, 21 nov 2018 anni – 1 gen 1962 anni)

Descrizione:

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.

Aggiunto al nastro di tempo:

Data: