Using Variables Control Charts
Two types of charts are used to track
variable data; one for averages and one for ranges. These charts are
commonly used together and are known as an X-bar & R Chart.
The Chart monitors the process
center, or location.
The R Chart monitors the
process variation, or dispersion.
As the data points for each subgroup are plotted, the
points are connected to the previous point and the charts are
interpreted to determine if one of the out-of-control patterns has
Typically, only one of the charts will go out-of-control
at any one time.
Remember to add a comment on a chart to indicate
the action taken to correct an out-of-control situation.