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356 Part V: Appendices
EXAMPLE B.11
Consider the data on the diameter measurements of ball bearings used in the wheels of
heavy construction equipment shown in Table 19.3 of Example 19.4 in Chapter 19, page
266. Then use the following steps to construct the X – and R control chart.
Solution:
1. Enter all the data in column C1 of the Worksheet window. Note that one has
the option to enter the data in rows of columns such that each row contains data
from one subgroup. This option is usually preferred when the sample size is
variable. Thus, we shall consider this option for constructing an X – and R control
chart with unequal sample sizes.
2. Click Stat from the command menu.
3. Select Control Charts in the pull-down menu under the Stat command menu.
4. Select Variable Charts for Subgroups from the Control Charts command menu.
5. Click on Xbar-R in the Variable Charts for Subgroups command menu. The dialog
box titled Xbar-R Chart shown in Figure B.14 appears immediately.
6. In the dialog box Xbar-R Chart choose the option “All observations for a chart
are in one column.”
7. Enter C1 in the next box.
8. Enter the sample size in the box next to Subgroup Sizes.
9. In the dialog box titled Xbar-R Chart there are several options available such
as Scale and Labels. Thus, for instance, if you select the Label option a new
dialog box will appear where you can enter the title of the X – and R chart and
any footnotes that you would like to see on the output of the X – and R chart and
then click OK. By default the title will be such as X-bar and R Chart for C1 or X-bar
and R Chart for “name of the variable” if you have given such name in column C1
of the data window. Use the option Xbar-R Options, for example, if you want to
specify the values of the population mean and population standard deviation
instead of estimating the population mean and population standard deviation by
using the given data. Then, click OK in the Xbar-R Chart dialog box. The desired
X – and R control chart will appear in the Session window. Thus, in our example
the Xbar-R Chart dialog box will look as shown in Figure B.14.
Continued
Shewhart X – and R Control Chart When Process Mean m and Process Standard
Deviation s Are Known. Follow the first eight steps given in Example B.11. Then
in step 9, click Xbar-R Options. A new dialog box, shown in Figure B.15, will
appear. Enter the specified values of the mean and the standard deviation in the
boxes next to Mean and Standard Deviation respectively, and then click OK.
Then, again, click OK in the Xbar-R Chart dialog box. The desired X – and R control
chart will appear in the Session window.