canal which would pass through a mountain range and connect the Xiang and Lijiang rivers. The result of this project was the Lingqu Canal, complete with thirty-six lock gates, and since it closely follows a contour line (i.e. following the contours of the natural saddle in the hills), it is the oldest known contour canal in the world. Counting rods: Counting rods are instruments used for performing calculations, which uses a grid of cells to represent a decimal position system. Each digit (0-9) appears as a tally of rods with red rods designated as positive numbers and black rods designated as negative numbers. Archaeological evidence of counting rods dates back to the 2nd century BCE. The earliest pictorial depiction of counting rods appears on Warring States period ceramics excavated in Dengfeng in Henan. The oldest surviving counting rods are bamboo rods discovered in a Han dynasty tomb at Fenghuangshan in Hubei, which dates to the reign Emperor Wen of Han. The first explicit textual description of counting rods is recorded in the Book of Han compiled by Ban Gu from around 60 CE, but there has been speculation regarding textual references as early as the 3rd century BCE. For example, one passage in the Tao Te Ching mentions that "a person good at shu [calculations] does not use bamboo tallies and bamboo slips." Crank handle: The earliest known depicted crank handle in art comes from a Han Dynasty (202 BC – 220 AD) green-glazed pottery tomb model of a farmyard, complete with a rotary grain mill, a man operating a foot tilt hammer for pounding grain, and to his left a winnowing machine with a crank handle used to operate the fan. The crank handle in later Imperial China (Tang and Song dynasties) was also used in grain mills, silk-reeling and hemp-spinning machines, the hydraulic-powered flour-sifter, the hydraulic powered bellows, the water well windlass, and other devices. Crossbow and repeating crossbow: According to British art historian Matthew Landruss and Gerald Hurley, Chinese crossbows may have been invented as far back as 2000 BC, while the American historian Anne McCants at the Massachusetts institute of Technology speculates that they existed around 1200 BC. In China bronze crossbow bolts dating as early as the mid 5th century BC were found at a State of Chu burial site in Yutaishan, Hubei. The earliest handheld crossbow stocks with bronze trigger, dating from the 6th