Labs

Satnav devices

The only meaningful way to test a satnav is to use it in a car, on real roads. And that's exactly what we do, clocking up a few hundred miles along the way. Our test route includes a starting point, several stops along the route and a destination specifically chosen to comprise a good mix of densely packed urban streets, suburban roads, busy motorways and hard-to-find country lanes, with many alternative routes for the software to choose from to get us there. In every journey, we deliberately take some wrong turns (always at the same point) to see how quickly the software recalculates a route.

Voice instructions are a crucial aspect - if these are clear and precise, there's little need to take your eyes off the road to look at the screen for guidance. The onscreen display is still important, though, and we evaluate each application for map clarity and how well journey information is conveyed. We also look at how easy it is to change settings and enter an address using a finger, since it's much more convenient than getting out the stylus. Lastly, we grapple with the in-car mounting systems to find out which are a breeze to use and which are a nightmare.

Back in the Labs, we press every button, select every option and change every setting, to find out exactly what the systems are capable of and how responsive they are. We enter a variety of addresses, using different search methods, to check out how easily and accurately the software finds the location we're looking for. We also assess the collection of POIs (points of interest), which identify places such as restaurants, hotels, airports and petrol stations. Plus, we check for any absent categories, such as cash machines or railway stations.

Then, we turn our attention to the hardware itself. Screen quality is of particular importance - not just the brightness from the backlight, but also the clarity outside in bright sunlight. Screens with glossy coatings lose marks for their reflectivity. The screen isn't only important if you use GPS on foot, but it can help in-car readability on sunny days too, especially when the sun is shining directly on the screen.

At the end of each review, you'll see four ratings: Performance, Features & Design, Value for Money and Overall. As ever, we don't simply pluck these figures out of the air: they're calculated using a mixture of objective scores and subjective quality ratings.

Performance

The Performance score is derived from a combination of our timed tests, as well as the accuracy of each device out on the road and its ease of use. The rating also includes the responsiveness of the GPS receiver and the general speed of the device's operation.

Features & Design

The Features & Design rating takes into account a variety of aspects: the maps and points of interest included, the size of the screen, the accessories and software included, the warranty and any wireless technologies including TMC modules. We also reward removable batteries and the device's portability. Other aspects that can't be measured objectively such as the quality of the screen are also factored in.

Value for Money

The Value for Money score is based on a weighted combination of the Performance and Features & Design scores. We then factor in the price including delivery for a bang-per-buck result.

Overall

Finally, the Overall score is a straight average of the other three ratings. It may appear slightly higher or lower than expected due to rounding.