This tab in the Add/Edit Variable dialog box controls the optimization options for the variable being edited or defined. The Add/Edit Variable dialog box is opened when you click on the Add or Edit button on the Variables page of the Circuit Settings dialog box.
Allow optimization of this variable: Select this checkbox if you wish to be able to use this variable when performing an optimization. When this checkbox is selected, the Minimum and Maximum text entry boxes are enabled. Enter the range of values you wish to allow for the variable during the optimization. For more details on Optimization, please see the Optimization page of the Circuit Settings dialog box.