Chinese abacus, early to mid 19th century.
© Science Museum / Science & Society Picture Library
The modern form of Chinese abacus appeared in the 13th century. This example is of a type common in the 19th century. It is intended for use in base 16, with each bead above the bar being worth five units and each bead below the bar being worth one unit. On the back is a 72 times table from 11 to 40.