The Garmin Forerunner 645 is a good quality GPS watch built primarily for runners. It has built-in music storage a solid selection of sports features, advanced running dynamics and support for Garmin running power.

The Forerunner 745 is a significant upgrade on the Forerunner 645. Support for open water swimming, triathlon tracking, and cycling power meters are massive upgrades, but the list doesn’t end there. The FR745 also has a pulse oximeter (to measure blood oxygen levels),personalized workout recommendations, and a better battery life.
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