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| XCHART Statement |
| See SHWXCHR in the SAS/QC Sample Library |
You can save the control limits for an 
chart in a SAS data set; this enables you to apply the control limits
to future data (see "Reading Preestablished Control Limits"
) or modify the limits
with a DATA step program.
The following statements read measurements from the data set PARTGAPS (see "Creating Charts for Means from Raw Data" ) and save the control limits displayed in Figure 42.2 in a data set named GAPLIM:
title 'Control Limits for Gap Width Measurements';
proc shewhart data=partgaps;
xchart partgap*sample / outlimits = gaplim
nochart;
run;
The OUTLIMITS= option names the data set containing the control limits, and the NOCHART option suppresses the display of the chart. The data set GAPLIM is listed in Figure 42.7.
The data set GAPLIM contains one observation
with the limits for process PARTGAP. The variables
_LCLX_ and _UCLX_ contain the lower
and upper control limits for the means, and
the variable _MEAN_ contains the central line.
The value of _MEAN_ is an estimate of the
process mean, and the value
of _STDDEV_ is an estimate of the process standard deviation
.The value of _LIMITN_ is the nominal sample size associated
with the control limits, and the value of _SIGMAS_ is the
multiple of associated with the control limits.
The variables _VAR_ and _SUBGRP_ are bookkeeping variables
that save the process and subgroup-variable.
The variable _TYPE_ is a bookkeeping variable that indicates
whether the values of _MEAN_ and _STDDEV_ are estimates
or standard values.
The variables _LCLR_, _R_, and _UCLR_ are not used
to create charts, but they are included
so the data set GAPLIM can be used to create an R chart;
see Chapter 43, "XRCHART Statement."
If you specify the STDDEVIATIONS option in the XCHART statement,
the variables _LCLS_, _S_, and _UCLS_ are included
in the OUTLIMITS= data set. These variables can be used to create
an s chart; see Chapter 44, "XSCHART Statement."
For more information, see "OUTLIMITS= Data Set" .
You can create an output data set containing both control limits
and summary statistics with the OUTTABLE= option, as illustrated
by the following statements:
title 'Summary Statistics and Control Limit Information';
proc shewhart data=partgaps;
xchart partgap*sample / outtable=gtable
nochart;
run;
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This data set contains one observation for each subgroup sample. The variables _SUBX_ and _SUBN_ contain the subgroup means and sample sizes. The variables _LCLX_ and _UCLX_ contain the lower and upper control limits, and the variable _MEAN_ contains the central line. The variables _VAR_ and SAMPLE contain the process name and values of the subgroup-variable, respectively. For more information, see "OUTTABLE= Data Set" .
An OUTTABLE= data set can be read later as a TABLE= data set.
For example, the following statements read GTABLE and
display an chart (not shown here)
identical to the chart in Figure 42.2:
title 'Mean Chart for Gap Widths';
proc shewhart table=gtable;
xchart partgap*sample;
label _SUBX_ = 'Gap Width';
run;
For more information, see "TABLE= Data Set" .
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