X bar R Charts in Excel
Use an X bar R chart to evaluate stability of processes using variable data--time, cost, length, weight.
Here is an example of an X bar R chart in Excel (Average and Range Chart) created using the QI Macros SPC Software.
X bar R chart data usually looks like this:
The XbarR chart can help you evaluate the cycle time for almost any process: making a widget, answering a customer call, seating a customer, delivering a pizza, or servicing an appliance. This chart is especially useful when you do this many times a day. Collecting the data could be expensive if you measured every time you did it. Using a small sample (typically two to five), however, you can effectively measure and evaluate the process.
Calculate, plot, and evaluate the range chart first. If it is "out of control," so is the process. If the range chart looks okay, then calculate, plot, and evaluate the X chart.
Please note: If you are asked by QI Macros for a "Subgroup Size," a subgroup is a group of measurements produced under the same set of conditions.