How did the yard as a unit of measurement originate?

Historically, units of measurement were derived from various parts of the body (the foot, the thumb, the forearm, etc.). According to tradition, a yard, measured on King Henry I (1068-1135) of England, was the distance from his nose to the middle fingertip of his extended arm. Other measures were originally derived from physical activity. For example, a league was the distance covered by walking for one hour; an acre was the amount of ground plowed in a day; a furlong was the length of a plowed ditch; and the ell, used to measure cloth, was the distance from the elbow to the tip of the index finger. These units, for obvious reasons, were very imprecise. The ell, for example, ranged from 0.513 to 2.322 meters depending on where it was used and the type of goods being measured. Below is a list of U.S. customary measures that originated in the...  more