TomTom One

Editors' rating: Aftermarket in-car devices
We rate in-car audio, video, and GPS devices on a scale of 0 through 10 (see "What the numbers mean" below). The editors calculate the overall rating from three subratings, on a scale of 1 to 10, that gauge key aspects of the device.

The rating criteria, with weightings, are as follows:

Features
(30 percent of the total rating)
Here we take into account built-in connectivity and media playback options, such as the number of sources the system can support, including the potential for extra features such as Bluetooth hands-free calling or satellite radio via add-on modules. We also look at the range of audio output features (such as a connection for a separate subwoofer) and the number of audio customization options the system offers. For advanced multimedia devices, we evaluate video playback options, and for GPS-enabled systems, we look at the number of programming options and the availability of advanced features such as real-time traffic reports and text-to-voice technology. When evaluating a system's features, we take into account its price relative to those of competitors in the category.

Design
(30 percent of the total rating)
A major factor here is the physical usability of the system from a driver's perspective. High marks are awarded for systems with intuitive interfaces, while complicated control systems score poorly. As part of the design evaluation, we look at the structure of file and folder navigation, the size and brightness of the display, and the layout of buttons and touch screen menus. For GPS-enabled systems, we look at the rendering and resolution of maps and the ease of programming in destinations. Price has no bearing on the evaluation of design; if a system works well, no matter how simple, it achieves high marks. Conversely, even if a system has an impressive feature set, it still has to be easy to use.

Performance
(40 percent of the total rating)
This rating deals with how well the head unit operates in real-life situations. To judge a head unit's audio performance, we listen to the receiver using standardized test speakers. In playing back different audio sources, we look for surround-sound effects, low-frequency effects, sound-field depth, and the effectiveness of preset and user-configured equalizer settings. We also use this rating to evaluate the functionality of Bluetooth hands-free calling, A2DP stereo Bluetooth audio streaming, and other advanced features. For GPS-enabled systems, we test the system on the road in a variety of situations, looking for factors such as accuracy, refresh rate, and ease of programming and canceling route guidance. When evaluating a system's performance, we take into account its price relative to those of competitors in the category.

What the numbers mean

10.0 (Perfect):
This exceedingly rare score is reserved for a product that is as perfect as it could be.

9.0 to 9.9 (Spectacular):
A product that receives a rating in this range scores high on all of its rating criteria. It succeeds at meeting all of its intended users' needs and has no meaningful drawbacks.

8.0 to 8.9 (Excellent):
A product that receives a rating in this range is superior in so many ways that its relatively few drawbacks are not very important.

7.0 to 7.9 (Very good):
While the strengths of a product scoring in this range certainly outweigh its weaknesses, it has some minor faults that certain users should be aware of.

6.0 to 6.9 (Good):
This range represents a product that is above average. Its strengths slightly outweigh its weaknesses, making it good for most uses but not a standout.

5.0 to 5.9 (Average):
A product that scores in this range is functional but unremarkable.

4.0 to 4.9 (Mediocre):
Products in this range are below average. They fall in the middle of the pack for most features, but suffer from a few additional major flaws.

3.0 to 3.9 (Poor):
You probably should not consider a product in this range or lower. There may be one or two specialized circumstances, however, that could justify the purchase of this product for a very low price for a specific demand.

2.0 to 2.9 (Terrible):
A product that receives a rating in this range scores low on all of its rating criteria. It does not satisfy any of its intended users' needs and has no meaningful strengths.

1.0 to 1.9 (Abysmal):
A product in this range should never have been produced. This product has no redeeming qualities and worse, may actually harm you or your productivity.