Variable Control Chart Results - X-bar Tab

Select the X-bar tab of the Variable Control Chart Results dialog box to access the options described here. The options on this tab will always pertain to the highlighted (selected) variable in the list of variables at the top of the dialog.

Specify limits

Select whether you want to specify the chart limits (UCL, LCL) in terms of a Multiple of sigma or p (probability), or as a Constant value.

Multiple of sigma

With this option, you can specify that the upper or lower control and upper and lower warning limit be calculated by multiplying z times sigma (traditionally, 3 times sigma is the recommended value). You can use the default value for z, or specify the value by typing the number into the box or using the microscrolls.

Computed from p

With this option, you can specify a probability on which to base the upper or lower control limit, as well as upper and lower warning limits (if selected). Note that the actual control limits will always be based on the respective normal distribution values, i.e., when establishing the control limits (as a multiple of sigma), the p value entered here will be converted to the respective normal z value, which is then applied to the computation of the control limits.

Constant value

With this option, you can enter a specific value to use as the upper or lower control limit and specific values for the upper and lower warning limits by typing the number into the respective edit fields.

Control limits X

Specify the Lower and Upper control limits for the X or X-bar chart. The values entered into these fields will be interpreted by the program in a manner consistent with the selection in the Specify limits box.

User defined

Use these options to specify user-defined values for the X-bar (X) Center line and/or Sigma.

Center line

Select this check box to specify a user defined center line value for the X-bar or X chart.

Sigma

Select this check box to specify a user defined sigma value for the chart.

Warning limits X

Use these options to specify warning limits for the X-bar (X) chart; note that the values entered into the respective fields will be interpreted by the program in a manner consistent with the selection in the Specify limits box.

Show warning lines (X-bar)

Select this check box to specify Lower and Upper warning limits for the X-bar (X) chart.