lower control limit

The lower control limit is a key component of statistical process control, a method used to monitor and maintain the quality of ongoing processes, such as manufacturing. Control charts, which are graphical displays, are central to this method. They help determine if variations in a process's output are due to random, common causes or identifiable, assignable causes.

The lower control limit, along with an upper control limit, is typically set at three standard deviations below the process mean. When sample data points fall within these limits, the process is considered to be in control. If a data point falls below the lower control limit, it signals an out-of-control condition, indicating that corrective action is needed to bring the process back to acceptable quality levels.12