Guinness: bamboo slips world’s oldest calculator

The world’s first decimal calculator was not electronic at all.
Bamboo slips more than 2,300 years old were officially recognized by the Guinness Book of World Records as the world’s earliest decimal calculation tool.
Each of the 21 slips, made around 305 BC during the Warring States Period (475-221 BC), is 43.5 cm long and 1.2 cm wide.
Arranged together as a multiplication table, they can do multiplication and division of any two whole numbers under 100, as well as numbers with the decimal 0.5.
Researchers surmise that the tool might have been used in trade or to measure land in the kingdom of Chu.