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Project Management & Agile · Foundational

Control Chart

A graph showing process data over time against a mean and upper and lower control limits to determine whether a process is stable.

Definition

Control limits are typically set at plus or minus 3 standard deviations from the mean. A process is out of control when a point falls outside the limits or when the rule of seven (seven consecutive points on one side of the mean) occurs.

Example

Weekly defect counts plotted with UCL 12 and LCL 2 show one point at 15: investigate special cause.

Exam tip

Control limits come from the process; specification limits come from the customer.

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