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358 Part V: Appendices
Shewhart X – and S Control Chart—Equal Sample Size. First enter the data in one
column, say C1, of the Worksheet window. Then from the command menu select
Stat > Control Charts > Variable Charts for Subgroups > Xbar-S. The dialog box
titled Xbar-S Chart shown in Figure B.16 appears immediately. We illustrate the
construction of a Shewhart X – and S control chart with the following example.
EXAMPLE B.12
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 S control chart.
Solution:
1. Enter all the data in column C1 of the Worksheet window. Note that as in the
case of the X – and R chart, 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 S control chart with unequal sample sizes.
2. Click Stat in 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-S in the Variable Charts for Subgroups command menu.
The dialog box titled Xbar-S Chart shown in Figure B.16 appears immediately.
6. From the Xbar-S Chart dialog box 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 entitled Xbar-S 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 S chart and
any footnotes that you would like to see on the output of the X – and S chart and
then click OK. By default the title will be such as Xbar-S Chart for C1 or Xbar-S
Chart for “name of the variable” if you have given such name in column C1 of the
data window. Use the option Xbar-S 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-S Chart dialog box. The desired X – and S
control chart will appear in the Session window. Thus, in our example the
Xbar-S Chart dialog box will look as shown in Figure B.16 and the output of
the X – and S chart will appear as shown in Figure 19.9 of Chapter 19, page 273.
Continued