Selecting the right control chart starts by knowing something about what you want the chart to say about the process—what questions do you want the chart to answer? Another way to look at this is to ask yourself, “Why am I collecting data on this part?” The answers to these questions will provide necessary information to determine the sampling strategy, sample size, and any special needs that would require implementing special processing options that extend the function of traditional charts.

Some folks like to use control charts to analyze gauge study results. When using a control chart in this manner, one can assume that the chart should represent a series of gauge studies conducted over a period of time. In this example, let’s say that each morning a gauge is verified by recording five repeated measurements of a certified gauge block.