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:
