X bar R Chart Formulas
The X bar R chart can help you evaluate the stability of processes using variable data--time, cost, length, weight when you have 2 to 10 samples per period.
Here are the X bar R chart formulas used in the QI Macros for both the Range and Average (Xbar) charts.
Conforms with ANSI/ASQC B1, B2, B3 1996
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.
Note: Some people wonder why the QI Macros results are a tiny bit different from some versions of other software. The answer is that they use a different estimator. Donald Wheeler in Advanced Topics in Statistical Process Control says: "Even though the Pooled [Standard Deviation] estimator is common in many applications, the robustness of Rbar/d2 and Sbar/c4 makes them the preferred estimators for use with process behavior charts."
- Create a X bar R chart in Excel using the QI Macros
- X bar R chart video
- X bar R chart template in Excel
- Other control chart formulas
The X bar R chart is just one of the tools included in the QI Macros for Excel SPC Software for Excel.