Revision as of 09:00, 6 November 2014

The Garmin 620 is an intriguing device, adding some cool advanced features but it has appalling GPS Accuracy that prevents me recommending it. This is a real shame as other than the accuracy problems I love using the 620. However, I've had the 620 record only 12 miles on a 13 mile run, something that I consider unacceptable.

The Garmin 620, showing the display of Cadence, Vertical Oscillation and Ground Contact Time. Note that the display is color, but I found the colors muted and not always easy to distinguish.

1 Garmin 620 Pros

• The 620 is small and light, but the display is quite legible for its size. I find it much easier to read than either the 610 or the 10.
• Like the Fenix 2, the 620 will show and record Cadence, Vertical Oscillation (VO) and Ground Contact Time (GCT). The 620 has a nice display of Cadence, VO, and GCT that gives a color coded indication of how well you're doing.
• Like several other devices, the 620 displays Training Effect, an indicator of how hard or effective a training session is.
• The 620 includes an estimation of the Recovery Time before the next workout, just like the Fenix 2.
• The 620 will cache the locations of the GPS satellites for the next few days, which will reduce the satellite acquisition time when travelling to a new location. In my usage the satellite acquisition was very rapid.
• The touchscreen works better than any other I've tried while running.
• There is a prediction of your V̇O₂max, which worked well for me, but I would not rely on its accuracy.
• The 620 will upload your workouts to Garmin Connect via WiFi without needing a computer. It will also link to a smart phone to upload a workout as it takes place, which is nice for folks tracking you during a race, though it means wearing the watch and the phone together.
• The 620 will cache the locations of the GPS satellites for the next few days, makes for faster satellite lock. However, if you've not connected the 620 to the internet for a few days, the 620 can be painfully slow to acquire a lock.
• The 620 will not display Heart Rate Variability but it is possible for it to record Heart Rate Variability for later analysis. To enable this recording, you need to download a special FIT file from the firstbeat.com web site.

2 Garmin 620 Cons

• The GPS Accuracy of the 620 is grim. I found the 620 consistently worse than the 610 or the 310XT when I ran with multiple devices. The 620 would sometimes be over a mile out on a 13 mile run!
• To make the poor GPS accuracy even more annoying, there is no way of displaying your current pace from the Footpod while using GPS for overall distance and course. (Earlier versions of the firmware would always display the pace and distance from the Footpod when it's connected, but this was fixed in a recent update.)
• The 620 includes an internal accelerometer to give you an idea of pace and distance while running on a treadmill without a footpod. While firmware updates have improved the accuracy, I found it was too far out to be of any use, giving a display that was off by 1-3 minutes/mile. A lot will depend on your running style and how you use a treadmill.
• There is no map display or navigation, but on a device this small it would be hard to make that useful anyway.
• 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 Training Effect with the older Garmin HRM, but not Ground Contact Time or Vertical Oscillation.

3 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:

1. 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.
2. 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".

3.1 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.

1. 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.
2. 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.
3. 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.

4 Comparison Table

I evaluate running watches in three distinct ways. Firstly, you can use a watch on its own, without any kind of Footpod. This is probably the most common way runners use their watch, but you miss out on a lot. The second rating is with a standard Footpod that is available quite cheaply. These Footpod's can be reasonably accurate once the calibrated, but calibration is a little tedious. The final evaluation is with the Stryd Footpod, which is vastly more accurate than any other type of Footpod, or and more accurate than GPS. The table below looks at the score, and the value for money of each watch for each of the three conditions. (I’ve also tested the Apple Watch 3, but I’ve not included it in these tables as it’s not really a running watch.)

The score is the sum of how well each watch can answer the four basic questions (how far, how fast, where are you, what's your cadence), plus some bonus points.

1. The "How far you've run" will be based on GPS only for "without Footpod" and "with Standard Footpod", but based on Stryd if supported in the "with Stryd Footpod" table..
2. How fast you're running assumes you're using a Footpod if it's supported, otherwise the rating is 0-2 based on GPS accuracy.
3. The "Where are you?" is based on various navigation features such as back to start, breadcrumbs, and preloaded maps. For some watches, you have to turn GPS off to get the benefit of Stryd, so those watches have worse "where are you scores" with Stryd than without.
4. The cadence score uses 1 point for an internal cadence sensor, 2 points for footpod support, 1 point for support from chest strap cadence, and 1 point for cadence alerts.
5. I give 1-2 bonus points for application support, 1-2 bonus points for data upload, 1-2 bonus points for Optical Heart Rate Monitoring, and 0-1 bonus points for battery life.
6. Value for money is the score divided by the price (at the time I last updated the table.) Your needs may be different, so you might weight the different aspects of the watches differently, or be basing your decision on different criteria totally. Hopefully this table will give you a good starting point for your decision.

4.1 Score Breakdown without a Footpod

4.2 Score Breakdown with a Standard Footpod

4.3 Score Breakdown with a Stryd Footpod

4.4 Basic Features

5 Navigation Features

For "navigation":

• Color Maps gives you full color maps, rather like a smart phone, with roads and paths marked out.
• Track Outline is a display of where you've run, rather like a breadcrumb trail. If there are maps, the outline is superimposed otherwise this is just the outline on its own without any context.
• Course Outline is an outline of a route that can be downloaded. I've found this useful during ultras or in unfamiliar cities where I've needed to know where to go.
• Back To Start is a simple arrow point to your starting point, so it won't help you backtrack.
• Back To Waypoint returns you to a previously marked location using a simple arrow to point.
• Compass. A magnetic compass can help you orient yourself or the map. Without a magnetic compass you have to be moving for the GPS to give you a sense of direction.

(Older Reviews: Polar RC3 GPS, Soleus 1.0, Motorola Motoactv.)