Control limits are based on the performance of your process, and tell you about the variability in your process. Upper control limits (UCLs), center lines, and lower control limits (LCLs) are calculated from the data when a control chart is created. You can use these calculated control limits to tell you when your process has changed and adjustments need to be made.
It is important to note that control limits are different from specification limits, which are often used in capability analysis.
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Control Limits |
Specification Limits |
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Calculated from data |
Given by customer or design |
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Based on variability |
Based on system requirements |
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Applied to summary statistics |
Applied to individual measurements |
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Applied to process measurements, perhaps on product, perhaps not |
Applied to product characteristics |
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The voice of the process |
The voice of the customer |