Geocaching is built on a beautifully simple idea: use GPS coordinates to find hidden treasures around the world, but the magic behind those coordinates depends on an incredibly sophisticated system of satellites, timing signals, and Earth models.
Selective Availability (SA) was an intentional degradation of GPS signals by the U.S. government, reducing civilian accuracy to 100 meters, which was officially discontinued in May 2000. President Clinton removed SA to make GPS more accessible for commercial use, improving precision to under 20 meters.