A 2,000-year-old Wangmang caliper unearthed in an Eastern Han tomb in Hanjiang County, Jiangsu Province， is exhibited at the National Museum of China. (PHOTO:VCG)

By BI Weizi

One of the priceless exhibits at the National Museum of China in Beijing is a 2,000-year-old caliper unearthed in an Eastern Han tomb in Hanjiang, a county in Jiangsu province, east China. Almost identical to the calipers used today, it was named the Wang Mang caliper after its inventor Wang Mang (45 BC-23 AD), who was the emperor of the nAew Han dynasty, as well as a reformer and statesman.

The Wang Mang caliper scotched the erroneous claim by some Western scholars that French mathematician Pierre Vernier was the first person to invent the caliper in 1631, which was called the Vernier caliper after him. It caused the Encyclopedia Britannica to amend its entry on the Vernier caliper in 1973.

Though how it was invented remains a mystery, the Wang Mang caliper is one of the most advanced measuring instruments in the history of science and technology and very similar to the Vernier caliper people use today.

The caliper consists of two rulers, a fixed and a movable one. The fixed ruler is 13.3 cm long and has a fish-shaped handle on its upper end. The handle has a groove in the middle with a rotating and adjustable pin and can be moved left or right along the groove. The small, movable ruler is attached to the main ruler with a movable grip called a jaw. It can be moved along the main ruler by opening the jaw. The movable ruler has a thumb screw which provides a grip for moving it.

An object is measured by placing it between the caliper's jaws and moving the sliding jaw until the object is firmly gripped between two jaws. The measurement is then obtained from the readings on the two rulers.

The reign of Wang Mang saw extensive research on weights and measures, which led to the formation of China's traditional theory of weights and measures and had a profound influence on later generations.