Years ago, we used to joke about certain renowned canoeist, famous for these long distance journeys thousands of miles in length, who was going to have an odometer installed in his canoe. Ironically, on this trip, we'll have an odometer, speedometer, and compass installed in ours.
The Global Positioning System allows users to pinpoint their exact location anywhere in the world 24 hours a day. Originally, this system was designed for the U.S. military but was made available to recreational and outdoor users through hand held GPS units. There are 24 orbiting satellites that transmit signals containing time and orbital data that handheld units receive and calculate to determine exact position to within 20 ft. The GPS unit needs to acquire signals from at least three satellites to determine a position on the surface of the earth. A fourth signal is required to get three-dimensional positioning which determines elevation or altitude.
We are using the Garamin eTrex, one of the smallest GPS units available. Powered by two AA batteries, the eTrex allows programming of waypoints and will keep track of speed, elevation, position, and actual distance traveled, also projecting distance, bearing and arrival time to the next waypoint. We should mention that a GPS is no substitute for knowing how to navigate. We have never used any sort of navigational device (aside from a map and compass) on any previous trip and a GPS is not what we would call an essential item, but it does offer the convenience of calculating distance and elevation on a continuous basis. It will also settle any argument about exactly how far we paddled in a day.