Bamboo slips oldest decimal calculator, Guinness certifies

Bamboo slips more than 2,300 years old were recognized on Sunday by Guinness World Records as the world's earliest decimal calculation tool.

The 21 slips, crafted around 305 BC during the Warring States Period (475-221 BC), are each 43.5 centimeters long and 1.2 cm wide.

When arranged together as a multiplication table, the slips can perform multiplication and division of any two whole numbers under 100 and numbers with a fraction of 0.5.

The slips have inscribed numbers, and holes where threads used to go. A user would pull the threads corresponding to the numbers needed to be calculated to see the result. The owner of the slips is unknown.

"Our guess is that the tool might have been used in trade or in the measurement of land in the kingdom of Chu," said Li Xueqin, head of the Research and Conservation Center for Excavated Texts at Tsinghua University.

In July 2008, Tsinghua acquired a rare collection of 2,500 items from the late Warring States Period that had been smuggled out of China, including the multiplication table.

"It was the day summer vacation started, and we had planned to take care of the bamboo slips afterward," 84-year-old Li said. "When I opened the plastic box that held the bamboo slips, I saw they were quite muddy and I smelled harsh chemicals."

Small spots of mold were also growing on some of the slips. "If not immediately dealt with, the mold would have resulted in holes in the slips," said Zhao Guifang, an expert on bamboo slip protection at Tsinghua.

Li felt the job couldn't wait.

"Since they are made of bamboo, they had actually become as soft and fragile as tofu after 2,300 years," he said.

He and his team of more than 10 people started cleaning the slips with the smallest and softest brushes. They spent the next four months cleaning the 2,500 slips day and night.

Cleaning was just the beginning. Preserving the slips also posed challenges for the team. To keep them in good condition, they had to be put in distilled water at a constant temperature. The water had to be changed daily.

The team now meets to read the slips every Monday morning. Apart from the multiplication table, the bamboo slips also hold about 65 ancient records recognized as among the most important artifacts from the Warring States Period.

"They survived the book burnings of Qinshihuang, China's first emperor, who united the country. Therefore, they have great research value," Li said.