Example 5.19 Displaying a Normal Reference Line

[See CAPPROB4 in the SAS/QC Sample Library]Measurements of the distance between two holes cut into 50 steel sheets are saved as values of the variable Distance in the following data set:

data Sheets;
   input Distance @@;
   label Distance='Hole Distance in cm';
   datalines;
 9.80 10.20 10.27  9.70  9.76
10.11 10.24 10.20 10.24  9.63
 9.99  9.78 10.10 10.21 10.00
 9.96  9.79 10.08  9.79 10.06
10.10  9.95  9.84 10.11  9.93
10.56 10.47  9.42 10.44 10.16
10.11 10.36  9.94  9.77  9.36
 9.89  9.62 10.05  9.72  9.82
 9.99 10.16 10.58 10.70  9.54
10.31 10.07 10.33  9.98 10.15
;
run;

The cutting process is in control, and you decide to check whether the process distribution is normal. The following statements create a normal probability plot for Distance with lower and upper specification lines at 9.5 cm and 10.5 cm:

symbol v=plus height=3.5pct;
title 'Normal Probability Plot for Hole Distance';
proc capability data=Sheets noprint;
   spec lsl=9.5 usl=10.5;
   probplot Distance / normal(mu=est sigma=est)
                       square
                       nospeclegend;
run;

The plot is shown in Output 5.19.1. The MU= and SIGMA= normal-options request the diagonal reference line that corresponds to the normal distribution with estimated parameters and . The LSL= and USL= SPEC statement options request the lower and upper specification lines. The SYMBOL statement specifies the symbol marker for the plotted points, and the

Output 5.19.1 Normal Reference Line

request the diagonal