GPS watch

GPS watches are most often used for sports and fitness purposes.

Some GPS watches can also be used as display.

For instance, fitness trackers feed step counts and even sweat rate into their equations, while GPS watches lean heavily on heart rate.

Runners who wore GPS watches start e-mailing him or posting comments on Facebook or Twitter afterward.

In addition to the half-marathon error, runners in the 10 km race reported that their GPS watches measured that race's length as approximately 9.7 km.

TomTom Runner GPS Watch, $170 Navigation company TomTom knows GPS, so it's not a surprise the company wants to help runners improve their routes this summer.

The devices range from simple fitness trackers (FitBit Ultra, Nike+ FuelBand, BodyMedia Link) to GPS watches (Motorola MotoACTV, Garmin Forerunner 910XT, Polar RCX3) that communicate wirelessly with sensors pasted all over my body.