inch). With such accuracy and the ubiquity of the service, GPS has evolved far beyond its original military purpose and has created a revolution in personal mercial navigation. Battlefield missiles and artillery projectiles use GPS signals to determine their positions and velocities, but sodo the U.S. space shuttle and the International Space Station as well mercial jetliners and private airplanes. Ambulance fleets, family automobiles, and railroad otives benefit from GPS positioning, which also serves farm tractors, ocean liners, hikers, and even golfers. Many GPS receivers are no larger than a pocket calculator and are powered by disposable batteries, while puter chips the size ofa baby's fingernail have been installed in wristwatches, cellular telephones, and personal digital assistants
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