Step 1: Preliminary Mean and Standard Deviation Charts

The following statements create and charts for the diameter data:

symbol h=3.0 pct;
title f=qcfont1 'X ' f=none 'and s Chart for Diameter';
proc shewhart data=toolwear;
   xschart Diameter*hour /
      outhistory = submeans
      nolegend ;
   label Diameter = 'Mean in mm';
   label hour     = 'Hour';
run;

The charts are shown in Figure 13.43.48. The subgroup standard deviations are all within their control limits, indicating the process variability is stable. However, the 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.

Output 13.43.48 and Charts for TOOLWEAR Data

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