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Closed-Center-type Load Sensing Systems for fluid power controls in hydraulic excavators, which had been considered as far back as 1955, were proposed in the U.S.A. in 1975, but were not feasible. In the late of 1980's European-made hydraulic excavators were equipped with load sensing systems, including flow dividing control. In the early 1990's, further improvement of CLSS's were made in Japan. CLSS's are capable of controlling complex motions of multiple actuators with high accuracy against varying loads under varying engine speed conditions, with expectations for improved controllability and compatibility of hydraulic excavators to many kinds of works in which attachments are used. Conversely, operators have made the best use of the characteristics of conventional fluid power systems, in which each actuator speed is varied by inertia or engine speed change.