The Reason Your GPS Is Always Slightly Wrong — and the Fix

5. The Selective Availability Legacy - Intentional Inaccuracy and Its Lasting Effects

For the first two decades of GPS operation, the most significant source of positioning error was entirely intentional. The U.S. military implemented a policy called Selective Availability (SA) that deliberately degraded the accuracy of civilian GPS signals by introducing random errors into satellite clock data and orbital information, limiting civilian users to positioning accuracy of approximately 100 meters. This artificial degradation was designed to prevent potential adversaries from using GPS for precise military targeting while still allowing civilian applications like general navigation and surveying. President Bill Clinton ordered the discontinuation of Selective Availability in May 2000, instantly improving civilian GPS accuracy from 100 meters to approximately 3-5 meters and triggering an explosion of GPS-dependent technologies and applications. However, the legacy of SA continues to influence GPS design and user expectations in subtle ways. The civilian GPS signal structure and receiver designs developed during the SA era were optimized to work despite intentional signal degradation, and many of these design choices persist in modern systems. Additionally, the dramatic improvement in accuracy following SA's removal created unrealistic expectations among users who began to expect GPS to be perfectly accurate, leading to frustration when the remaining sources of error became more apparent. The SA experience also established important precedents for civilian access to military-grade positioning systems and continues to influence international discussions about satellite navigation system governance and access policies.