Once Rbar is determined, control limits for average can be calculated. Control charts where n is variable. As specified, use Table F, Appendix 3. Used frequently for seasonal products, and best used when process changes slowly. Plotting individual values along with standard average of subgroup provides a useful picture that helps to show variation among subgroup data points and also is good for training purposes.
Control limits are the same as always.
Control charts can be plotted using average of the medians and average of the ranges, or using the median of the medians and medians of the ranges. Different factors are used for each. Also called action limits provide secondary rules for course of action to take. Combination rules i.e. so many in a row between center line and outer limit, plus outside of outer limit. Use standard probability calculations.