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SCHART Statement |

See SHWSEX1 in the SAS/QC Sample Library |

In some applications, a standard value may be available for the process standard deviation .This example shows how you can specify to compute the control limits.

Suppose that the amount of power needed to heat water
in the heating process described
at "Creating Standard Deviation Charts from Raw Data" has a
known standard deviation of 200.
The following statements specify this known value and create
an *s* chart, shown in Output 40.1.1,
for the power output measurements
in the data set TURBINE:

title 's Chart for Power Output'; title2 'Using Known Process Standard Deviation of 200'; symbol v=dot c=salmon; proc shewhart data=turbine; schart kwatts*day / sigma0 = 200 ssymbol = s0 cframe = vligb cinfill = ywh cconnect = salmon; run;

The SIGMA0= option specifies ,and the SSYMBOL= option specifies a label for the central line indicating that the central line is computed from .Since all the points lie within the limits, you can conclude that the variability of the process is stable.

You can also specify as the value of the variable _STDDEV_ in a LIMITS= data set, as illustrated by the following statements:

data plimits; length _var_ _subgrp_ _type_ $8; _var_ = 'kwatts'; _subgrp_ = 'day'; _type_ = 'STDSIGMA'; _limitn_ = 20; _stddev_ = 200; run; title 'Chart Using Known Process Standard Deviation'; symbol v=dot; proc shewhart data=turbine limits=plimits; schart kwatts*day / ssymbol=s0; run;

The resulting *s* chart (not shown
here) is identical to the one shown in Output 40.1.1.
For more information,
see "LIMITS= Data Set" .

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