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Publication date: 07/30/2020

Work with Control Limits

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.

Table 3.9 Control Limits versus Specification Limits

Control Limits

Specification Limits

Calculated from data

Given by customer or design

Based on variability

Based on system requirements

Applied to summary statistics

Applied to individual measurements

Applied to process measurements, perhaps on product, perhaps not

Applied to product characteristics

The voice of the process

The voice of the customer

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