Mxsmanic wrote:
Newps writes:

A satellite is a satellite. The information that spews forth from that
satellite is just information that my receiver makes use of.

Hardly. GPS satellites are very special, as are the transmissions
they produce. WAAS satellites are just commercial satellites
transmitting fairly ordinary information in fairly ordinary ways.

WAAS consists of approximately 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 corrected
differential message is then broadcast through one of two geostationary
satellites, or satellites with a fixed position over the equator. The
information is compatible with the basic GPS signal structure, which
means any WAAS-enabled GPS receiver can read the signal.

A WAAS-capable receiver can give you a position accuracy of better than
three meters 95 percent of the time.
http://www.garmin.com/aboutGPS/waas.html
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- gpsman