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* The battery life is a little short for ultramarathons, but it is fine for the most runners.
* You need to have the new HRM for the new features. It will display Heart Rate and calculate [[Firstbeat| Training Effect]] with the older Garmin HRM, but not Ground Contact Time or Vertical Oscillation.
=GPS Accuracy Issues=
The Garmin 620 has some well-known [[GPS Accuracy]] issues that are mostly shared with the [[Garmin Fenix 2]], which both use the MediaTek GPS chipset. I've seen two types of problem with the 620:
# Generally mediocre performance, though this obviously varies. Occasionally the Fenix 2 will be quite good, as you'd expect from a random level of error.
# The 620 records the right shape track, but offset by some distance. This does not look like a typical accuracy problem that would manifest itself randomly.
Note that the 620 does not have the Fenix 2 problem of reporting "lost satellite reception".
==Is It Just Some Watches?==
Some people are quite happy with the accuracy of their 620 or [[Garmin Fenix 2]], prompting speculation that this is a quality control issue and the problems only effect some devices. I don't believe this is the case for a number of reasons.
# I've tested 5 devices (2x Fenix 2,3x 620) that exhibit the problem. It seems remarkably unlikely that 5 out of 5 devices would have the problem. The problems with these devices seem remarkably similar, though only the Fenix 2 has the catastrophic 'lost satellite reception' problem.
# The severity of the problem depends on the situation. Running a fairly straight course with a wide open view of the sky is likely to give pretty good results.
# Awareness of the problem will depend on testing methodology. Few users gather enough data to be statistically significant, or run on a course that's certified. Even running on a certified course, it's tough to hit the tangents perfectly unless you're a front runner.
=Comparison Table=
{{:Best Running Watch-table}}