GPS Accuracy – What’s right and what’s not


Technology is meant to make our lives easier, not harder. We live in a world where information is just a few key clicks away, and yet technology is not always perfect. GPS technology has been around in some capacity for decades, and athletes have been able to take advantage of it en masse for a little over 10 years. While the technology from all brands, has drastically improved over this time period, we still see variances between the watches (technology) and the analog measurements (think about your local 5k or half marathon route).

We have seen feedback from many COROS users over the last few weeks suggesting that COROS watches – PACE and APEX are “under-measuring” runs. i.e. our watches are suggesting that the runner has covered less distance than the readings of some of our competitors. So who is right? As human beings, we always want to believe we went farther and faster as opposed to shorter and slower – that is just how our psychology works. In addition, we as consumers are susceptible to what is known as the status quo bias – we believe that the larger more established brands must be right or best, only because they are the largest and best known. This bias also makes us less likely to believe that a newer and lesser known company could be more accurate.

Despite these various biases, we have seen in our testing that COROS is most accurate when compared to all of the major competitors including the industry leader. Let’s look at some case studies which compare the COROS APEX to one of the top selling models from the industry’s leading GPS watch brand.

  • Below is an example of a road run – this is an environment where GPS signal is generally quite strong. Even our team was surprised by how much COROS APEX outperformed the industry leader.

    • Overview map. Orange is COROS APEX, Blue is the industry leader’s high-end multi-sport watch. The runner runs out and back along the same route. COROS APEX (9.02 miles) vs Industry leader (9.18 miles)

    • With a closer look at the GPS data track, runners are actually running on the paved trail (white lines) and APEX (Orange) puts the track nearly right on target. Meanwhile the competitor is off by roughly 3-6 feet.
    • Additionally, we look where the path has major curves and goes through a tunnel. The competitor is significantly off under the bridge where there was no GPS signal for both watches while APEX holds close to the proper route.
  • Similar to this – as watches are pinging satellites thousands of miles away, old GPS technology may create a path that has more zigzags than you have actually run, which can result in an increased distance being displayed. As you can see on the map above, COROS has found a way to provide a smoother “path” on the GPS output, which results in a more realistic/accurate measurement
    In DC rainmaker’s recent review, he mentioned:

While he doesn’t know the reason, we do. The Garmin track has far more zigzags than the APEX. Runners are often running in much more of a smoothed line, rather than the zigzags shown by Garmin in the his review. See the track detail below, Orange is the COROS APEX

  • The reality of running on various terrain is that sometimes watches will lose connection to satellites (whether they tell you they have lost connection/regained connection or not). When connection is lost, most brands show you as having run a straight line from point to point. COROS has multiple sensors including an accelerometer and a gyroscope and compass which not only allow the watch to use its learning from your runs with clear signal to determine your pace and distance, but it also can determine your turns and changes in elevation. This all leads to the best possible measurement in areas of traditionally low connectivity (like trails because of all of the tree cover) Now let’s look at a more complex trail in the Grand Canyon.
    • Overview. Orange is COROS APEX and Blue is a high-end outdoor watch from the industry leader. COROS APEX (20.0 miles) vs Industry leader (21.66 miles)

In the beginning, APEX (in orange track) was performing better than the competitor (in blue track) and recorded fewer miles than the competitor did in the windy trail.

APEX (orange) outperformed the competition in this section. Even though the terrain is difficult with high mountains close by, APEX delivered accurate tracking.

APEX (orange) showed its capability again at handling windy and technical terrain.

APEX and the competitor both encountered a difficult section with low GPS signal and difficult terrain. However, APEX was able to accurately record the tracking around the Ooh Aah Point.

APEX (orange) tracked accurately for the majority of this section.

Both watches performed relatively well in the non-windy parts of the route. For the windy routes, APEX performed better than the competitor in general. There are places where both watches found challenging and some spots that the competitor outperformed APEX. In conclusion, more accurate tracking in windy routes is the main reason why APEX recorded 1.66 miles fewer than the other watch.

  • Finally, as crazy as it sounds, sometimes watches add distance even when you are not moving (if your watch itself is not stopped but you are). As the watch continues to try to ping the next satellite, it is more or less guessing that you are still moving. While this may not amount to much, if you stop in your runs frequently (like at traffic lights), or perhaps are stopping at an aid station during an ultra, you may see an increase in distance even when you are not moving. COROS has engineered its technology to avoid these “phantom miles”

    • This is an example of us using two watches hanging out chatting for 10 mins outside of our office building. While we were not moving at all, APEX recorded 0.2 km but Garmin Forerunner 935 recorded 0.8 km.

Below we can also see the GPS track recoding. As you can see both watches showed some movement, but the APEX in Blue was much more stable.

As you can see, COROS has made every effort to produce the best and most accurate GPS watch on the market. That said, there is always room to get better. Being the leader in GPS accuracy, we still find that improvements can be made in heavy urban areas, rocky canyons and stadium tracks. We will continue to put out updates to further improve accuracy and the overall user experience. We certainly hope you will enjoy exploring with COROS.