A unit is a collection of I/O devices in a physical box; a string is a collection of units containing I/O devices. You can create, edit or delete units within a selected string. First, open the String dialog by double - clicking on a string in the configuration diagram, choosing the String... command from the Edit menu, or selecting a string and pressing the Edit... button in the Strings/Devices section of the Controller dialog. Then click on the Edit... button in the String dialog to open the Edit String dialog. This dialog lists all units in the selected string. Create, edit or delete units by selecting one or more units and pressing the appropriate buttons in the Units section of the dialog.