How GPS Modes Affect Accuracy

By Joel McNamara

Part of GPS For Dummies Cheat Sheet

The accuracy of your GPS unit can vary depending on whether you set the mode to make use of differential GPS (DGPS), which augments satellite information with ground-based signals; a wide area augmentation system (WAAS) developed by the Federal Aviation Administration for more accurate air navigation; or go without selective availability (SA). The following table shows how accurate you can expect your GPS unit to be in each mode:

GPS Mode Distance in Feet Distance in Meters
GPS without SA 49 15
GPS with DGPS 10–16 3–5
GPS with WAAS 10 3