GPS is the U.S. Global Navigation Satellite System (GNSS). A network of 24 satellites continuously transmits high-frequency radio signals, containing time and distance data that can be picked up by any GPS receiver, allowing the user to pinpoint their position anywhere on Earth. (Magellan). GPS was originally called NAVSTAR (NAVigation System with Timing and Ranging). The first GPS satellites however that were available for civilian use had SA imposed (Selective Availability); the intentional distortion of GPS signals to prevent military adversaries from using the highly accurate positioning data. SA limited GPS to 100-meter accuracy for non-U.S. military users. In 2000, Selective Availability was turned off by presidential order (Clinton), giving all GPS receivers the potential accuracy of 15 meters without the use of signal correction. The signals are available 24 hours a day in any weather condition, everywhere around the world. When used with WAAS or EGNOS receivers, GPS accuracy can be improved to 3 meters.