Editing Touchscreen (section)

===Acoustic pulse recognition===
The key to this technology is that a touch at any one position on the surface generates a sound wave in the substrate which then produces a unique combined signal as measured by three or more tiny transducers attached to the edges of the touchscreen. The digitized signal is compared to a list corresponding to every position on the surface, determining the touch location. A moving touch is tracked by rapid repetition of this process. Extraneous and ambient sounds are ignored since they do not match any stored sound profile. The technology differs from other sound-based technologies by using a simple look-up method rather than expensive signal-processing hardware. As with the dispersive signal technology system, a motionless finger cannot be detected after the initial touch. However, for the same reason, the touch recognition is not disrupted by any resting objects. The technology was created by SoundTouch Ltd in the early 2000s, as described by the patent family EP1852772, and introduced to the market by [[Tyco International]]'s Elo division in 2006 as Acoustic Pulse Recognition.<ref>{{Cite journal|title=Acoustic Pulse Recognition Touchscreens|page=3|publisher=Elo Touch Systems|year=2006|url=http://media.elotouch.com/pdfs/marcom/apr_wp.pdf|access-date=2011-09-27|url-status=live|archive-url=https://web.archive.org/web/20110905005921/http://media.elotouch.com/pdfs/marcom/apr_wp.pdf|archive-date=2011-09-05}}</ref> The touchscreen used by Elo is made of ordinary glass, giving good durability and optical clarity. The technology usually retains accuracy with scratches and dust on the screen. The technology is also well suited to displays that are physically larger.