Right-click the object you want to connect and choose Link Variable to. The Variable Connections dialog box appears.
Click the parameter in left pane and click Next.
Expand the system or display folder and select the Variable you want to connect to.
TIP: To disconnect variables from parameters, access the Variable Connections dialog box for the object, select the parameter in the left pane, its associated variable in the right pane, and then click the Disconnect button.
NOTE: VariableLinks will display in the Variable Connections list for a given variable that they are showing. Removing this connection from the Variable Connection dialog box will disconnect the VariableLink so that it will no longer show the value.