Frank Zybach, a tenant farmer and inventor living near Strasburg, Colorado, received a patent for a "Self-Propelled Sprinkling Irrigating Apparatus" on July 22, 1952. The device used mobile towers to continuously move a pipeline in a circle around a pivot. Water was supplied through the pivot and distributed by sprinklers on the pipeline. Zybach formed a partnership with A.E. Trowbridge, an entrepreneur-businessman, in 1953 to manufacture center pivots in Columbus, Nebraska. In 1954 manufacturing rights were sold to Valley Manufacturing, starting a world-wide industry including several manufacturers. The center pivot was the first system capable of automatically, efficiently and uniformly irrigating a variety of crops, soils, sloping terrains and field sizes. Agricultural engineers have improved the safety, efficiency and dependability of the original design. The center pivot has become the most widely used method of sprinkler irrigation. By 1992 over 110,000 machines were being used to irrigate 14 million acres in the U.S. Center pivots have contributed to a dependable, high quality, food and fiber supply through efficient use of soil and water.