11.7. Control Charts for The Mean and Range

Variables control charts are used to study a process when a characteristic is a measurement; for example, cycle time, processing time, waiting time, height, area, temperature, cost, or revenue. Measurement data provides more information than attribute data. Therefore, variables charts are more sensitive in detecting special cause variation than are attribute charts. Variables charts are typically used in pairs. One chart studies the variation in a process, and the other studies the variation in the process mean. You must examine the chart that studies variability before the chart that studies the process mean. You do this because the chart that studies the process mean assumes that the process variability ...

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