I won't go into the details of how GPS works as there are a number of reviews round these parts that do a good job of explaining it. What i will do is explain why, after two years, I decided to upgrade my trusty old (bright yellow) garmin eTrex to a shiny new (silver) eTrex Summit.

Not wanting to cover too much old ground (and without trying to force too many more reads of an old review), the eTrex is a basic GPS device that is capable of storing up to 500 waypoints and a single route (which can be made of up to 50 waypoints). It maintains a tracklog and can allow you to retrace your steps and will let you navigate (using the word loosely) to any stored waypoint. but that's about it. So when you are going away for a week and won't have a PC with you, it can be a bit tricky working with a selection of routes. It's not unworkable, but it certainly isn't easy.

While the interface remains the same, the hardware (and software) has been upgraded from the base model. Whereas the base etrex would only give you a compass bearing when you were on the move, the Summit comes with an electronic compass for accurate bearings even when stationary. This does take it's toll on the battery life but can come in handy, especially when you have lost the GPS signal. In addition to the compass, the Summit also improves on the GPS-based altimeter function in the base model with the addition of a full barometric altimeter. This allows for a much more accurate plotting of elevation and gives an excellent calculation of ascent/descent rates (as well as warnings relating to sudden changes in air pressure and that could indicate a change for the worse in the weather). Both of these new functions come with their own GUI modes, the compass being the most familiar and the altimeter being the least useful, but it's all information and for the gadget-fans out there, it's good stuff.

So far, then, the Summit does everything the base eTrex can do and a few things more which make it much more useful for a hill walker/rambler type person. What the unit DOESN'T do is provide base-maps that you can use to navigate around unfamiliar territory. The Summit does have a map page, but all you will find on it are waypoints that you have marked and the track showing where you have been. It is very much a case of only getting out what you put in. Indeed it is the lack of base-map information that keeps the cost of the unit so low while still providing all the navigation features of the more expensive models. Where the Summit really does come into it's own is when it is used in conjunction with some mapping software on a PC (such as the excellent Memory-Map navigator). This allows you to create your own routes from Ordnance Survey maps and then upload them, waypoints and all, to the GPS for future use. It's then a simple task of selecting the appropriate route when you reach the start point and the GPS will guide you all the way round (if needed).