Use Moving Range
Chart to monitor the variation of your process when you have continuous data that are individual observations not in subgroups. Use this control chart to monitor process stability over time so that you can identify and correct instabilities in a process.
A hospital administrator wants to monitor whether the variation in surgery times is stable. Because the data are not collected in subgroups, the administrator uses a moving range chart to monitor the variation of the surgery times.
Where to find this control chart
To create a moving range chart, choose Stat > Control Charts > Variables Charts for Individuals > Moving Range.