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A steelyard balance or steelyard is a straight-beam balance with arms of unequal length. It incorporates a counterweight which slides along the calibrated longer arm to counterbalance the load and indicate its weight. A steelyard is also known as a Roman steelyard, or Roman balance.
The steelyard comprises a balance beam which is suspended from a pivot (or fulcrum) which is very close to one end of the beam. The two parts of the beam which flank the pivot are the arms. The arm from which the object to be weighed (the load) is hung is short and is located close to the pivot point. The other arm is longer, is graduated and incorporates a counterweight which can be moved along the arm until the two arms are balanced about the pivot, at which time the weight of the load is indicated by the position of the counterweight.
The steelyard exemplifies the law of the lever, wherein, when balanced, the weight of the object being weighed, multiplied by the length of the short balance arm to which it is attached, is equal to the weight of the counterweight multiplied by the distance of the counterweight from the pivot.
According to Mark Schiefsky of Harvard University, the steelyard was in use among Greek craftsmen of the 5th and 4th centuries BCE, even before Archimedes demonstrated the law of the lever theoretically. Roman and Chinese steelyards were independently invented around 200 BCE. Steelyards dating from 100 to 400 CE have been unearthed in Great Britain. Steelyards and their components have also been excavated from shipwrecks of the Byzantine period in the Mediterranean and the Red Sea, such as the 7th-century wreck at Yassi Ada, Turkey, and the mid-first millennium shipwreck at Black Assarca Island, Eritrea. The Oxford English Dictionary suggests that the name "steelyard" is derived from the Steelyard, the main trading base of the Hanseatic League in London in the 14th century.
Steelyards of different sizes have been used to weigh loads ranging from ounces to tons. A small steelyard could be a foot or less in length and thus conveniently used as a portable device that merchants and traders could use to weigh small ounce-sized items of merchandise. In other cases a steelyard could be several feet long and used to weigh sacks of flour and other commodities. Even larger steelyards were three stories tall and used to weigh fully laden horse-drawn carts.
With sliding pivot
A Scandinavian steel-yard is a variant which consists of a bar with a fixed weight attached to one end, a movable pivot point and an attachment point for the object to be weighed at the other end. Once the object to be weighed is attached to its end of the bar, the pivot point, which is frequently a loop at the end of a cord or chain, is moved until the bar is balanced. The bar can be calibrated so that the object's weight can be read off directly from the position of the pivot. This type is known in Sweden, Denmark and Norway.
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