The XRS charts display trends of subgroup means (X bar), ranges (R) and standard deviations (s). The XRS chart operates similarly to a standard trend, but with additional SPC extra features. Each subgroup displays as a single node on the graph and consecutive nodes are linked by a line.
Each control chart has a central line and two control limits-upper and lower (UCL and LCL). CitectSCADA automatically calculates these SPC values at run-time. If you want to override the UCL and LCL you can do so by entering the Process Mean, Range, and Standard Deviation fields in SPC Tags.