Humminbird 755C Marine GPS System User Manual

How GPS and Cartography Work
Your 700 Series™ Chartplotter supports GPS and chartplotting, and uses GPS
to determine your position and display it on a grid. The Global Positioning
System (GPS) is a satellite navigation system designed and maintained by the
U.S. Department of Defense. GPS was originally intended for military use;
however, civilians may also take advantage of its highly accurate position
capabilities, typically within +/- 10 meters, depending on conditions. This
means that 95% of the time, the GPS receiver will read a location within 10
meters of your actual position. Your GPS Receiver also uses information from
WAAS (the Wide Area Augmentation System), EGNOS (the European
Geostationary Navigation Overlay Service), and MSAS (the MTSAT Satellite
Augmentation System) satellites if they are available in your area.
GPS uses a constellation of 24 satellites that
continually send radio signals to the earth. Your
present position is determined by receiving signals
from up to 16 satellites and measuring the
distance from the satellites.
All satellites broadcast a uniquely coded signal
once per second at exactly the same time. The GPS
receiver on your boat receives signals from
satellites that are visible to it. Based on time
differences between each received signal, the GPS
receiver determines its distance to each satellite.
With distances known, the GPS receiver
mathematically triangulates its own position.
With once per second updates, the GPS receiver
then calculates its velocity and bearing.