#### X Tilde & R Chart

A type of Subgroup Chart that plots median and range. The X Tilde & R Chart consists of two charts: the upper chart is a plot of the subgroup medians, with out-of-tolerance points in a red color; the lower chart shows the subgroup range. Two additional statistical parameters, CP and CPK, also appear on the chart.

The X Tilde & R Chart yields similar conclusions as the XBar & R Chart, but the median is more robust in that one outlier within the subgroup does not affect the median. For subgroups with an odd number of members, the median is the middle value. For subgroups with an even number of members, the median is the average of the two central values.

See also:

- Control Limits for X Tilde & R Charts

- Capability Indices: Table of Calculations

- Process Chart