Step 1: Preliminary Mean and Standard Deviation Charts

Graphical Enhancements

Step 1: Preliminary Mean and Standard Deviation Charts

The following statements create $\bar{X}$ and s charts for the diameter data:

   title f=qcfont4 'X ' 
         f=swiss   'and s Chart for Diameter';
   symbol v=dot c=salmon;
   proc shewhart data=toolwear;
      xschart diameter*hour /
         outhistory = submeans
         nolegend 
         cframe     = vibg
         cinfill    = ywh
         cconnect   = salmon;
      label diameter = 'Mean in mm';
      label hour     = 'Hour';
   run;

The charts are shown in Figure 47.23. The subgroup standard deviations are all within their control limits, indicating the process variability is stable. However, the $\bar{X}$ chart displays a nonlinear trend that makes it difficult to decide if the process is in control. Subsequent investigation reveals that the trend is due to tool wear.

Figure 47.23: $\bar{X}$ and s Charts for TOOLWEAR Data

Note that the symbol $\bar{X}$ is displayed in the title with the special font QCFONT4, which matches the SWISS font used for the remainder of the title. See Appendix D, "Special Fonts in SAS/QC Software" for a description of the fonts available for displaying $\bar{X}$ and related symbols.

Chapter Contents
Previous
Next
Top