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XRCHART Statement |

See SHWXR3 in the SAS/QC Sample Library |

By default, the XRCHART statement estimates the process mean () and standard deviation ()from the data, as in the previous example. However, there are applications in which standard values ( and ) are available based, for instance, on previous experience or extensive sampling. You can specify these values with the MU0= and SIGMA0= options. For example, suppose it is known that the adhesive coating process introduced in the previous example has a mean of 1260 and standard deviation of 15. The following statements specify these standard values:

title 'Specifying Standard Process Mean and Standard Deviation'; symbol v=dot c=salmon; proc shewhart history=tape; xrchart weight*sample / mu0 = 1260 sigma0 = 15 xsymbol = mu0 cframe = bigb cinfill = ywh cconnect = salmon; run;

The XSYMBOL= option specifies the label for the central line on
the chart.
The resulting and *R* charts are shown in Output 43.2.1.

The central lines and control limits for both charts are determined using and (see the equations in Table 43.22). Output 43.2.1 indicates that the process is in statistical control.

You can also specify and with the
variables _MEAN_ and _STDDEV_ in a LIMITS= data set,
as illustrated by the following statements:

data tapelim; length _var_ _subgrp_ _type_ $8; _var_ = 'weight'; _subgrp_ = 'sample'; _type_ = 'STANDARD'; _limitn_ = 5; _mean_ = 1260; _stddev_ = 15; proc shewhart history=tape limits=tapelim; xrchart weight*sample / xsymbol=mu0; run;

The variables _VAR_ and _SUBGRP_ are required, and their
values must
match the *process* and *subgroup-variable*, respectively,
specified in the XRCHART statement.
The bookkeeping
variable _TYPE_ is not required, but it is recommended to
indicate that the variables _MEAN_ and _STDDEV_ provide
standard values rather than estimated values.

The resulting charts (not shown here) are identical to those shown in Output 43.2.1.

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