A product review by Bobulous.
Product made by Garmin. A GPS unit uses the Global Positioning System of satellites to work out where you are on Earth, and where you're heading.
Including a Garmin-brand belt-pouch, I paid £260 at ASK Electronics on Tottenham Court Road for my GPS-III.
To work out where you are, a GPS unit needs to measure the signal strengths of certain satellite. So you need a clear view of the sky for the GPS to be of use. I first tried my sleek new unit (GPS unit, that is) on the train home after I bought it. I don't know about other train lines around the world, but the Victoria to Sutton line is often sunk into landscape, rows of trees on banks either side. So I didn't get a consistent signal and the unit only once managed to work out my position on the map.
Off the train, though, was a different story. Given a clear set of signals from at least three satellites (there are twenty-four in orbit all around the Earth), the unit can lock your position to within fifty metres (about 160 foot), anywhere on Earth. Given a wide open sky you'll end up with signals from about eight satellites and then the accuracy gets very impressive, pointing to your location to about fifteen metres' accuracy (about 50 foot). People of Europe will end up buying the International (i.e. non-US) version which has map data that includes coastlines, all major cities, major rivers and lakes, main roads, and political borders for regions all over the world. And within Europe the map display has more detail, including as many towns, smaller rivers and lakes, and lesser roads as they could cram into the thing. It's no A-Z, but with all these reference points it is very easy to work out where you are.
As you travel with the unit monitoring your position, a "breadcrumb trail" of track markers is laid down on the map. At any point you can save this track and activate TracBack mode which will give you very clear directions to head back the way you came. You can leave named waypoints (and there's room for up to 500) at important positions on the map and plan routes using them. The unit will estimate time to next waypoint on a route, and total time before finishing a route, all along giving you a pointer arrow to show you which way to go.
The map display isn't the only mode, though, and you're offered a compass view, a "highway" mode, a position display, and screens that let you load / save / create routes, check on satellite signal status and battery power, and alter the setup of the unit. All together, the views inform you about: your current speed, average speed and maximum speed; current direction and optimum direction (to get to next waypoint); exact time by UTC; position in one of several formats (e.g. longitude & latitude); and, if you're reading enough well-positioned satellites, altitude. All units are selectable (because half the world uses metric measurements, and half uses the awful imperial set of distances). Combine all this with the map, and the amount of information is very impressive.
On a trip to Staffordshire (North England) I brought the GPS-III with me and put it on the dashboard, the stubby little bar-antenna pointing up through the glass of the windscreen. The signal you get while driving along main roads is superb, and even small forest-roads with sporadic overhanging trees give good results. In fact, the only time the signal failed was while travelling through a two-hundred metre tunnel. Speed readings are very close to those offered by the car speedometer, and the map's display of motorway junctions made it very easy to work out which way to go. On the way home, the TracBack function worked incredibly, giving directions to an accuracy that seemed unbelievable at times.
The unit itself does not let down the software it supports. The case is light and small enough to be handheld, but is very solid and waterproofed to IPX7 standards. The display screen is clear and spacious and easy to read in all types of light. And it comes with a backlighting function that lets you navigate after dark, though this will consume the batteries at a faster rate. Talking of which, the battery life on my GPS-III managed 16.5 hours before the unit failed to run. Though this is very good, it's not the 24 hours that the sales clerk at ASK Electronics assured me was built in. The unit also accepts an antenna upgrade, for more precise positioning, though most people won't need this extra accuracy for general navigation.
The GPS-III is an incredible piece of equipment. I cannot think of anything wrong with the operation of it. Though not great for urban pedestrian use (difficult to travel as-the-bird-flies through streets and the unit is more easily confused by tall buildings and obstacles), it works superbly over long distances in a car, and is probably invaluable for hiking and rambling through remote and poorly landmarked areas. It would have been nice if the battery life was the 24 hours I'd been promised, but sixteen hours is certainly very good. Most of that energy consumption was part of a long car journey, and a separate in-car power adapter allows use of the unit without wasting batteries. The map detail is very good until you start wanting very specific detail like minor roads and locations of small towns, and the GPS-III software certainly isn't a route-generating tool (you can't tell it you want to go to Birmingham and expect it to produce a list of roads to take). But as a way of working out where you are and where you're going to end up, it's brilliant.
If you've decided a GPS system is just what you need, an excellent site to visit is Jack Yaezal and Joe Mehaffey's GPS Information, Software, and Hardware Reviews of Garmin, Lowrance, and Magellan. Or visit the Garmin site and see their product line.