How they work
When the monitor is turned on, a current runs through both of these layers and when they are forced to contact each other, such as with the pressure on them applied by a finger, the monitor driver software detects this connection and translates it into something that the computer can understand and it responds accordingly.
As one might imagine, having three layers on top of the glass layer could reduce the clarity and overall quality of the image passing through, not to mention the general loss of the emitted light from the monitor itself.
One of the benefits of this system is that the monitor can register the contact event between the two layers regardless of the device used to create that contact point. The human finger, a pen, or any other object can initiate this contact.
Surface Resistive and other Touchscreen Technologies Video Reviews
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GVision L15AX-JA 15" LCD Monitor with Capacitive Touchscreen - Black details $ 299.95