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An updated description of process control status using on-line computers at Martin Marietta Cement's Western Division plants at Tulsa, Okla, and Lyons, Colo., is presented. The company's approach to automation including training of plant personnel is briefly outlined. The Tulsa plant, which has had a General Electric GEPAC 4040 computer on-line since 1966, is discussed first. A brief summary of the computer hardware and software precedes a discussion on kiln control, cooler control, and raw mix proportioning control using the computer. The paper's coverage of the Leeds and Northrup 5200 computer installation at the Lyons plant is more extensive since it is of more recent vintage (late 1969 installation) and since it is used for direct digital control rather than used to drive the analog control set-points (DAC) as is the case at Tulsa. The hardware and software at Lyons is described in some detail. The DDC loops for the raw mill, the kiln, the cooler, and the finish mill are identified together with indication of the loop status and problems involved. Raw mix proportioning control is outlined briefly. The paper concludes with a discussion of the comparative advantages of DDC (versus DAC) and Martin Marietta's plans for future process control progress.