Which of the following is not found on an X-bar and R control chart?

An X-bar and R control chart is primarily used to monitor the mean and variability of a process over time. The key components that are typically displayed on these charts include the average (sample mean) of the sample data points and the range of the sample data, which helps to assess process consistency.

The sample mean is crucial as it provides information about the center of the process distribution. The range indicates the dispersion or variability within the samples, which is essential for understanding process stability.

The sample size is also relevant as it informs the number of data points used to calculate the sample mean and range, affecting how accurately the control limits are set.

In contrast, the capability ratio (also referred to as the process capability index) gives an assessment of how well a process can produce output within specified limits. This measure is not part of the X-bar and R control chart, which focuses on monitoring the process variations and averages rather than evaluating capability against specifications. Therefore, the capability ratio does not appear on an X-bar and R control chart.