How to do Example 3-7 on page 99 of Montgomery's Forth
Edition.
Make Cotton Percentage Nominal. Select Fit Model
from the Analyze menu. The following dialog box appears.
Notice that we made Strength the Y variable. We also selected Cotton Percentage and clicked on the Add button.
Click on the Run Model button. The resulting output
will include the following leverage plot:
Select Add Contrast... from the triangle menu on top of the leverage plot. The following dialog box will appear:
Click on the appropriate pluses and minuses for each contrast. For example
for 
click on the + next to 30 and on the minus next to 35. To add a
new contrast click on the New column button. With all four contrasts
entered the dialog box will look as follows:
Click the Done button. The following tables appears:
Compare this table with Table 3-12 on Page 99 of Montgomery's Forth Edition