This situation occurs when the standard deviation of the process at the various average values of the process is very small relative to the tolerance width, that is, the difference between the upper and lower specification limits. In usual statistical process control terms, such a process is not in control but may be able to produce acceptable product. As you read statistical literature, it will appear that three different kinds of charts are being generated for the aforementioned situation. These two issues are independent of each other. Acceptance Acceptance deals with the ability of a process to meet specifications.
Control deals with the ability of a process to perform in a consistent, stable fashion.
Some writers refer to the chart generated with an AQL-based design as a modified control chart, and others simply call it an acceptance control chart. Decide on the AQL appropriate for the process. Graphical Display of UAPM Step 3. Graphical Display of UAL Remember that the standard deviation of the ' s is the standard deviation of the x' s divided by the square root of the sample size, i.e., where n is the sample size. Example Suppose we have a process whose output is approximately normally distributed.