Results - X-Specs Tab

Select the X-specs tab of the Results dialog box to access the options described here.

Specifications for X-chart.

Set << >>

If you have more than one set, these buttons will be available to select which set you want to work with.

Center

Click this button to display the Chart center line dialog box, which is used to select the value of the center line of the respective chart instead of the default process mean value.

Sigma. Click this button to display the Sigma for dialog box, which is used to specify a particular value of the process sigma. Note that this value will also be readjusted if you change the center line for the variability chart; conversely, if the user changes the value of sigma, then the center line for the variability chart will also be automatically adjusted.

When you click the Sigma button, the respective Sigma dialog box will be displayed, in which you can specify the variability (sigma) for the respective quality characteristic (for example, for the X-bar chart). This value will be used in the control chart to establish the sigma limits.

Target values for sigma can be derived from experience or from previous similar processes. For a description of the computations involved in standard quality control charts, refer to Computational Details for Quality Control Charts.

UCL, LCL

Click these buttons to display either the Upper Control Limit dialog box or the Lower Control Limit dialog box, respectively, which is used to change the value of the Upper and Lower Control Limits from their default values of plus/minus 3 times sigma. The UCL (upper control limit) and the LCL (lower control limit) define the lines in the chart that are used to determine whether or not a particular sample statistic, and thus the entire process, is in control.  

Warning Lines

Click this button to display the Warning lines dialog box, which is used to specify warning lines. Warning limits are often established to alert the quality control engineer if minor deviations from the center line occur in some samples.

If Unequal n

This box is used to specify whether to base the chart on the average sample sizes (Use average n), to plot separate control limits for each sample (Use sep. limits), or to plot the standardized (normalized) deviations of the sample means from the target specification (Normalize chart). The average n procedure is satisfactory, as long as the sample sizes do not vary by more than 10%; otherwise, choose one of the two other settings.

Open Specs

Click this button to display a standard Open file dialog box, which is used to retrieve previously saved specifications (*.ini file) for the current variable (chart).  

Save Specs

Click this button to display the Select specifications to be saved dialog box. Click OK on this dialog to display a Save as file dialog, which is used to save your specifications as an *.ini file.

Moving average line. You can include a moving average line in the charts by selecting On. If you do not want to include a moving average line in the charts, select Off.

Process capability

Click this button to display the Specifications for Capability Analysis dialog box, which is used to select the values the capability analyses are based on.

Runs Tests

Click this button to display the Run Tests for Control Chart dialog box, which is used to select which test to perform. These tests are designed to detect patterns that may indicate that the process is out of control.