X Bar Chart Monitors. Variables Charts for Subgroups. The X with the two lines above X double bar is the overall average.
The control limits on both chats are used to monitor the mean and variation of the process going forward. These are used to monitor the effects of process improvement theories. These charts are used when the subgroups have large sample size and S chart provides better understanding of the spread of subgroup data than range.
The measurements of the samples at a given time.
Valves are 100 percent tested but for charting purposes the test results from three out of every 30 valves are used for analysis on control charts. The measurements of the samples at a given time. The other value of using this chart is that if there is no assignable-cause variation the process is to be left alone. Use this control chart to monitor process stability over time so that you can identify and correct instabilities in a process.
