Calculating chain for teaching

摘要

The chain has plastics discs numbered sequentially and strung on a line. The discs overlap each other on the chain and the computing involves clamping different coloured clamps (d) onto the appropriate discs. The different modes of calculation; addition, subtraction, multiplication and division, are represented by different colours of clamps. The linking string is threaded through two holes in each disc to form the simple overlay pattern.