On a Shewhart chart, upper and lower control limits are used to decide whether a point signals an out-of-control condition. On a cusum chart, the limits take the form of a decision interval or a ...

The central line on a Shewhart chart indicates the average (expected value) of the summary statistic when the process is in statistical control. The upper and lower control limits, labeled UCL and LCL ...

The top dashed line is the upper ... limits have been around for a long time. Walter Shewhart, a physicist at Bell ...