Declare the system stable or unstable
If your system is unstable, does the special cause of variation create a favorable output? Does it improve the process? If yes, find the special cause(s) of variation. Try to replicate it and incorporate it into the process.
If not, and it creates a negative output or hurts the process, find the special cause(s) of variation and take steps to eliminate it. After you remove special causes of variation, continue collecting, charting, and analyzing the data. Once the process has been stabilized, consider performing capability analysis to compare how the process is running in relation to its specifications.
If it does not fail any of the tests for control, the process is stable .
If your process is stable, is the data normal distributed ? Is it capable of producing output that is within specifications? You may want to create a histogram and perform capability analysis to learn more about your process.
Note: A process that is currently stable, may not remain stable indefinitely. A new batch of raw material, a new operator, or new equipment, can change the output. Therefore, you should continue collecting, charting, and analyzing data for stable processes.
Capability analysis can be done using software products such as SQCpack.