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GPSMAP 176/176C Owner’s Manual 81
APPENDIX > WAAS AND DGPS
What is WAAS?
The Wide Area Augmentation System (WAAS) is an F.A.A. funded
project to improve the overall integrity of the GPS signal. It is
a space-based system that broadcasts integrity information and
correction data as determined by ground reference stations. WAAS
testing completed in September of 2003 confirmed an accuracy of 2
to 3 vertical meters throughout the majority of the continental U.S.
and portions of Alaska. For more information, go to
http://gps.faa.gov/Programs/WAAS/waas.htm.
NOTE: If you are using the GPSMAP 176/176C outside of the
U.S., we recommend that you turn off WAAS for the most accurate
location fix.
What is Differential GPS (DGPS)?
The U.S. and Canadian governments (among others) have set up
Differential GPS (DGPS) stations to transmit correction signals. They
are operational in coastal areas and on many navigable river systems.
The DGPS system is available for use without a fee.
Please refer to the U.S. Coast Guard’s Web site,
http://www.navcen.uscg.gov/ for locations and the status of the
differential sites. Using DGPS requires additional equipment.