linguistic:paraphrasing, structural:reformatting
Hillside leveling

Hillside leveling, in which a hydraulic system re-orients the combine, allows combines to harvest steep but fertile soil. Their primary advantage is increased threshing efficiency. 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 thresh more efficiently. Secondarily, leveling changes a combine's center of gravity relative to the hill and allows the combine to harvest along the contour of a hill without tipping, a danger on steeper slopes; it is not uncommon for combines to roll over on extremely steep hills. Hillside leveling can be very important in regions with steep hills, such as the Palouse region of the Pacific Northwest of the United States, where hillsides can have slopes as steep as 50%.

The first leveling technology was developed by Holt Co., a US company in California, in 1891. Modern leveling came into being with the invention and patent of a level sensitive mercury switch system invented by Raymond Alvah Hanson in 1946. A leveling system was also developed in Europe by the Italian combine manufacturer Laverda. Gleaner, IH/Case IH, John Deere, and others all have made combines with a hillside leveling system, and local machine shops have fabricated them as an aftermarket add-on. Newer leveling systems do not have as much tilt as the older ones, as modern combines use a rotary grain separator which makes leveling less critical.