In establishing control limits for an R control chart, the lower limit (LCL) is always zero.

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Quizplus · Accepted Answer

The lower control limit (LCL) for an R control chart is not always zero. It depends on the variability of the process being measured. The LCL for an R chart is typically calculated as the average range of a subgroup multiplied by a factor determined from statistical tables. This factor (usually between 2.5 and 3.0) is chosen to ensure that the LCL is low enough to signal a possible problem with the process if the data falls below it. If the process has low variability, the LCL may be greater than zero.

In Establishing Control Limits for an R Control Chart, the Lower