WAAS is a great new technology that substantially increases the accuracy of your GPS. It tests for errors and fixes them, so that you can get a typical accuracy of less than 3 meters. Here’s how it works.
WAAS has about 25 “ground reference” stations positioned across the United States that monitor GPS satellite data. Two “master stations”, located on either coast, collect data from the reference stations and create a GPS “correction message”. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere.
The signal is then corrected and is then sent through one of two geostationary satellites, or satellites with a fixed position over the equator. The information works with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.
For now, you can only get WAAS coverage in North America, but it should become available to other places soon.
100 Meters was the accuracy of the original GPS.
15 Meters is the typical accuracy of a GPS withous SA
3-5 Meters is the accuracy for typical differential GPS(DGPS).
<3 Meters is the typical WAAS position Accuracy.