Understand that control limits are set at the target mean ± 3 standard errors, that the standard error shrinks as subgroup size grows, and that a larger subgroup size makes a control chart sensitive enough to catch smaller process shifts.
Standard error of the mean: SE = σ / √nControl limits: UCL = μ + 3·SE, LCL = μ − 3·SEOut of control: sample mean falls outside [LCL, UCL]Keep the process shift at 0. Confirm the sample mean sits exactly on target and well within the control limits.
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