3.11. Summary

Montgomery and Runger list 5 reasons why monitoring charts are widely used. After this section of the book you should understand the following about the charts and process monitoring:

1. These tools are proven to improve productivity (i.e. to reduce scrap and rework, as described above), and to increase process throughput.

2. They detect defective production, consistent with the concept of “doing it right the first time”, a mantra that you will increasingly hear in the manufacturing workplace.

3. A monitoring chart with good limits will prevent over-control of the process. Operators are trained not to make process adjustments unless there is a clear warning or alarm from the chart.

4. The patterns generated by the plots often help determine what went wrong, providing some diagnostic value to the operators. We will see a more formal tool for process diagnosis though in the latent variable section.

5. Monitoring charts are required to judge if a process is stable over time. A stable process allows us to calculate our process capability, which is an important metric for your customers.