Calipers

Calipers, sometimes spelled callipers, are an instrument used to measure the linear dimensions of an object or a hole, including its length, width, thickness, diameter or depth, typically by closing a pair of jaws around or inside the thing being measured and reading the result off a scale, dial or electronic display. The word caliper comes from a corrupted form of caliber, and the vernier caliper, one of the most familiar forms, takes its name from Pierre Vernier, who improved on an earlier graduated scale designed by the Portuguese mathematician Pedro Nunes. The earliest known caliper, with fixed and movable jaws, was recovered from the Giglio wreck off the Italian coast and dates to the sixth century BCE, and a bronze caliper from China's Xin dynasty, made around 9 CE, was inscribed with manufacturing details and graduated in inches and tenths. Calipers are used across mechanical engineering, metalworking, forestry, woodworking, scientific work and medicine wherever a precise linear measurement is needed.