The combine harvester is a machine that harvests grain crops. The name derives from its combining three separate operations comprising harvesting reaping, threshing, and winnowing into a single process. Among the crops harvested with a combine are wheat, oats, rye, barley, corn, sorghum, soybeans, flax, sunflowers, and canola. The waste straw left behind on the field is the remaining dried stems and leaves of the crop with limited nutrients which is either chopped and spread on the field or baled for feed and bedding for livestock. Combines some of them quite large were drawn by mule or horse teams and used a bullwheel to provide power. Later steam power was used and George Stockton Berry integrated the combine with a steam engine using straw to heat the boiler. At the turn of the twentieth century, horse drawn combines were starting to be used on the American plains and Idaho often pulled by teams of twenty or more horses. Hillside leveling has several advantages. Primary among them is an increased threshing efficiency on hillsides. Without leveling, grain and chaff slide to one side of separator and come through the machine in a large ball rather than being separated dumping large amounts of grain on the ground. By keeping the machinery level, the straw walker is able to operate more efficiently making for more efficient threshing. IH produced the 453 combine which leveled both side-to-side and front-to-back enabling efficient threshing whether on a hillside or climbing a hill head on.