The bushel is a volume measurement for grain created historically by Celtic peoples (Scotland, Wales, Brittany, Ireland) to facilitate fair grain trade. The bushel measurement was not defined originally in terms of cubic feet, but is currently considered to be about 1.25 cubic feet in volume. Although grain is referred to in terms of bushels in the United States, it is referenced and traded on the basis of weight in various metric designations throughout the rest of the world. To facilitate the trading of grain, the USDA created weight standards for each grain so that grain could be weighed to determine the number of bushels rather than trying to make volume measurements. Corn was assigned a bushel weight of 56 pounds, while soybeans and wheat were assigned bushel weights of 60 pounds. Some other examples are: Rye = 56 pounds per bushel, barley = 48, oat and fescue = 32, etc. The Test weight concept was developed some years back by the grain trade as a means of accounting for the varying densities of grain caused by weather and/or production practices. When grain density is lower than the accepted standard (low test weight), more volume is needed to store and transport a given weight of grain, thus increasing storage and transport costs. Different grades of each grain have different standard test weights. No. 2 yellow corn has a standard of 56 pounds per bushel while No. 3 yellow corn has a lower weight. Test weight is determined on each load of grain sold by weighing a known volume of the grain. If the weight is lower than the acceptable range, the sale is "docked" on a percentage basis. The seller of grain with test weight greater than the acceptable range is usually not rewarded for a superior product. Varieties of a crop often vary in their inherent test weight.