gen-briefly-explain-statistical-process-control-and-one-common-m-8e76

Briefly explain statistical process control and one common misconception about it.

# Statistical Process Control (SPC) **Statistical Process Control** is a method of monitoring and controlling processes using statistical tools to distinguish between normal process variation and abnormal signals that require intervention. It typically uses control charts to plot process data over time, with upper and lower control limits (usually ±3 standard deviations from the mean) that help identify when a process is "out of control." The goal is to maintain process stability and reduce variation, enabling predictive performance and preventing defects rather than just detecting them. ## Common Misconception **Control limits are NOT specification limits.** Many people confuse control limits (calculated from the process's natural variation) with specification limits (customer requirements or engineering tolerances). A process can be statistically "in control" but still produce defective products if its natural variation exceeds specifications. Conversely, a process may be "out of control" statistically but still meet all specifications. Control limits tell you about process *stability*, while specification limits tell you about process *capability*.