I’ve used my e-trex GPS unit for the past couple of years on many car and local-hiking trips, and a few backpacking journeys deeper into the country. This unit allows me to download Garmin’s road maps into the e-trex for car trips, and their topographic maps for backcountry trips. With this unit I can also save my trail’s GPS data onto my PC for either archiving or sharing. Things I don’t like: The PC software is not terribly intuitive, although it is usable with some practice. The high resolution greyscale LCD screen helps, but topo maps are still too detailed to read usefully on a small screen. The screen also takes a while to update when scrolling around complex maps. In short this is an inexpensive, compact, and lightweight way to get into GPS navigation with downloadable maps.
However, there are much better units available, witih fast color screens and great battery life. If you are going to buy one GPS unit, the Garmin 60c (reviewed here) is the one to get.
The e-trex is small and light, and an ideal second unit. I will continue to use mine for mountaineering when I want to log a trip while carrying the absolute least amount of weight.
The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hrs.