Unidentified, ostensibly a type of abacus

Unidentified object, suspected of being a type of abacus

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Unidentified object, suspected of being a type of abacus
Science Museum Group
© The Board of Trustees of the Science Museum

Unidentified object, suspected of being a type of abacus, or colour blindness test, comprising a metal plate supporting an 11x16 grid of adjustable metal slips, 1850-1939