This set of two charts is the most commonly used statistical process control procedure. Used to monitor process behavior and outcome overtime. Provides very good measures and allows the process owner to take decisions and to control the process.
X bar and R chart is a type of control chart used to monitor a variable's data when samples are collected at regular intervals from a business or industrial process. The chart is advantageous in the following situations:
1. The sample size is relatively small (say, n ≤ 10— x bar and s charts are typically used for larger sample sizes)
2. The sample size is constant
3. Humans must perform the calculations for the chart
The "chart" actually consists of a pair of charts: One to monitor the process standard deviation (as approximated by the sample moving range) and another to monitor the process mean, as is done with the x bar and s and individuals control charts.