Statistical Process Control (SPC) uses measurements over time to understand process variation and detect changes that may require investigation. A control chart plots data against a centre line and statistically derived control limits; patterns or points outside those limits can signal a process change. Control limits describe observed process behaviour and are different from product specification limits. SPC helps teams act on process evidence, but a stable process can still produce results outside customer specifications.
Related: 质量检查 · quality sampling.