We use touch screens everywhere: tourist kiosks, automatic teller machines, point-of-sale terminals, industrial controls. Half a dozen vendors, plus in-house departments at major manufacturers, produced $800 million worth in 2000. The market is growing because the interfaces are easy-to-use, durable and inexpensive.

Touch screens employ one of three physics principles for detecting the point of touch. Pressing a "resistive" design with a finger or other stylus raises a voltage. In "capacitive" models, a finger draws a minute current (this method is often used for cursor pads on notebook computers). In other designs, a finger or stylus interrupts a standing pattern of acoustic waves or infrared lights that blanket the surface.

This article was originally published with the title At Your Fingertips.

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