What is GPS?
http://www.garmin.com/aboutGPS/

Garmin Ltd.


This site from Garmin describes GPS systems and the way that they work. Topics include the accuracy of GPS, the 24 satellites that make up the GPS space segment, the two low power radio signals that GPS satellites transmit, and the sources of GPS signal errors.

This resource is referenced here:
Subject: Geography:Geospatial
Resource Type: Scientific Resources:Overview/Reference Work