XmR Control Charts (also known as ImR Control Charts) are Individual and Moving Range Charts. They are used when the subgroup size is one. This may be when logistic reasons prevent larger subgroups, but is more commonly when there is no basis for rational subgroups.
The chart is based on the moving range between consecutive samples:
Upper Control Limit


Lower Control Limit


Moving Range Chart


Upper Control Limit


Lower Control Limit


D_{4} and d_{2} are taken from standard tables, based on a subgroup size of 2:
