In the history of measurement many distance units have been used which were based on human body parts such as the cubit, hand and foot and these units varied in length by era and location. In the late 18th century the metric system came into use and has been adopted to varying degrees in almost all countries in the world. The oldest preserved measuring rod is a copper-alloy bar that dates from c. 2650 BCE and was found by the German Assyriologist Eckhard Unger while excavating at Nippur. Rulers made of Ivory were in use by the Indus Valley Civilization period prior to 1500 BCE. Excavations at Lothal (2400 BCE) have yielded one such ruler calibrated to about 1⁄16 inch (1. 6 mm). Ian Whitelaw holds that the Mohenjo-Daro ruler is divided into units corresponding to 1. 32 inches (33. 5 mm) and these are marked out in decimal subdivisions with amazing accuracy, to within 0. 005 inches (0. 13 mm). Ancient bricks found throughout the region have dimensions that correspond to these units.
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