Quotation from PC Magazine, online.
 

The Global Positioning System is now ten times more accurate than before.

By Alfred Poor May 18, 2000

"The Global Positioning System (GPS)... has become an important part of our business and recreational activities. With the flick of a switch in May, the U.S. government instantly made it about ten times more accurate.

Originally designed to provide navigation information for the military services, the GPS depends on a constellation of 24 satellites and five ground stations. In order to prevent the system from being so accurate that enemies could use it against us, the Department of Defense had been using selective availability (SA) to degrade the signal. As a result, civilian applications were limited to about 100-meter accuracy, while the military's own equipment was able to eliminate the SA errors.

Turning off SA has improved GPS accuracy for all users to from 10 to 20 meters. With SA enabled, reported positions could be as much as 300 feet distant from the actual ones--enough to cause a mapping program to place your car on a street parallel to the one you were actually on. With SA turned off, the resulting 30-foot accuracy is enough to determine whether your car is on one side of a divided highway or the other. This level of accuracy will provide many benefits, including faster response times by emergency services.

...Although the United States intends to make the GPS system available for free for worldwide use, the military retains the ability to enable SA distortion 'on a regional basis' if required for national security."