Early ivory rulers have been found in the remains of the Indus Valley Civilization which existed from 3000-1500 BC. Evidence shows that they were very accurate in their measuring and building as their smallest unit was approximately 1/16". Thse early units were often based on body parts such as the cubit, the length of the forearm, which could be divided down to one twenty-fourth - the width of the middle finger. It is believed that this measuring system was inhereted from the Egyptians by the Romans, who introduced the foot, equivalent to twelve inches. In 1851, Geman industrialist, Anton Ulrich, invented the folding ruler.