Quantitative Analysis for Management, 13/e
by Barry Render, Ralph M. Stair, Michael E. Hanna, Trevor S. Hale
15.3 Control Charts for Variables
Control charts for the mean, and the range, R, are used to monitor processes that are measured in continuous units. Examples of these would be weight, height, and volume. The -chart (x-bar chart) tells us whether changes have occurred in the central tendency of a process. This might be due to such factors as tool wear, a gradual increase in temperature, a different method used on the second shift, or new and stronger materials. The R-chart values indicate that a gain or loss in uniformity has occurred. Such a change might be due to worn bearings, a loose tool part, an erratic flow of lubricants to a machine, or sloppiness on the part of a machine operator. The two types of charts go hand in hand when monitoring ...
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