In some cases, especially when tool wear, tool changes, different material or component lots, or set-up changes cause predictable trends or shifts in the mean, an approach to process control that is more complex than the basic Shewhart chart may be necessary. Both the shifts and the trends due to tool wear can be controlled using I-MR Charts, in addition to whatever type of chart is used to control variation within each set-up or tool change. (ref Appendix A2). In such cases, as above, use the first four weeks of individuals data to calculate