A set of bamboo slips used more than 2,300 years ago has been confirmed by the Guinness Book of World Records as the world’s first decimal calculation tool.

The 21 slips, each measuring 43.5cm long and 1.2cm wide, were crafted around 305 BC during the Warring States Period, China Youth Daily and Xinhua reported.

They were used to perform calculation, allowing people to multiply and divide any two whole numbers under 100 and of certain fractions, the reports said.

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The 21 bamboo slips were donated in a set of more than 2,000 of them, by a Tsinghua University alumni in 2008, according to previous media reports.

The 21 slips stood out from the others in the set as they were the only ones inscribed with numbers in ancient Chinese characters. The others were inscribed with other Chinese characters.

Li Xueqin, an expert at Tsinghua University, said decimals were not used in European countries until the 15th century, Xinhua reported.

The bamboo slips might have been used for trade or for calculating the surface area of plots of land, Li said.

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The slips have been described as China’s earliest mathematical documents.

Before being recgonised by Guinness as the world’s first decimal calculation tool, they had previously been dubbed the world’s earliest artefact of a decimal multiplication table by an American maths historian, according to Nature journal.