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[[File:TomTomCardioRunner.jpg|none|thumb|200px|The TomTom cardio runner, showing the green LEDs that provide optical heart rate monitoring.]]

The key feature of the {{TomTom Cardio Runner}} is its optical measurement of heart rate, rather than requiring a separate chest strap. Other than that, the TomTom is a fairly mediocre device, and you're paying a premium over some of the better options listed here. I think that the TomTom is only worth considering if you really want the optical heart rate monitoring, otherwise look elsewhere.

* The optical heart rate monitoring works reasonably well. This technique has been around for decades, but it's only recently that the technology has been viable for use during exercise. The TomTom uses two green LEDs and a detector to determine Heart Rate based on the blood filling of the capillaries under the skin.

** When the watch has a good lock on your heart rate it's fairly accurate, and normally within a few beats/minute of a chest strap based monitor. Most of this variation seems to be due to the smoothing that's applied to the reading rather than overall accuracy.

* The TomTom can pair with a smart phone, allowing for posting of workouts or updating the satellite pre-cache via the phone.

* I rather like the TomTom's four buttons arranged as a square for input, which works rather like a joystick for navigating menus. The right side of the screen is touch sensitive for turning on the backlight or recording a lap, but it's triggered by sweat.

* The core functionality of the TomTom seems rather crude when compared with other devices in this price range.

* You can chose two metrics to display at the top of the screen, but these are shown in a tiny font that is hard to read in poor light.

|[[File:TomTomLED.JPG|none|thumb|x300px|The LEDs that detect heart rate optically. The lines you can see on the picture are not visible to the eye.]]

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These graphs show the TomTom Cardio Runner against the record of a traditional chest strap. The top of the graph shows the two recordings superimposed, with the TomTom in red and the chest strap in blue. The lower line on the chart is the difference between the two readings.

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