Generally, touch screen contains two vertically stacked transparent layers. Four-wire and eight-wire touch screen consists of two layers with the same surface resistance of transparent resistive material, five wires and seven wire resistive touch screen consists of a layer and a conductive layer, usually use of an elastic material to the two layers are separated. When the pressure on the touch screen surface (such as pressed by the pen or finger) is large enough, it will produce contact between the top and bottom. All resistive touch screen are used to generate a voltage divider principle on behalf of X and Y coordinates of the voltage. For a specific direction on the resistive touch screen coordinate measurement, the need for a resistive layer bias: its one side connected to VREF, ground on the other side. ( For more, please refer to http://tinyurl.com/ox5a2bq )