Creating Man-made Materials in Cycles - Blender Cycles Materials and Textures - page 161

Creating the exposed sockets

3. Add a Math node (press Shift + A and navigate to Converter | Math). Set Operation

to Subtract and first Value to 1.000 . Drag its second Value input socket to the Group
Input node, label the new socket as Coated , and then connect the Value output
to the Bright input socket of the Bright/Contrast node. In the Interface subpanel
under the Properties panel, set the Max value for the Coated socket to 1.200 ,
as shown in the following screenshot:

The setting of the Min and Max values through to the Interface subpanel