Polar Grit X Accuracy

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Here are some indicative test results from the Polar Grit X on the latest PRODUCTION firmware. There is not too much to comment on in that the GPS Accuracy has little changed from the Vantage series. The new Precision Prime oHR, if anything, is not yet quite as good as the previous version.

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For my personal sports data recording, I’ve given up trying to get accurate optical HR data and accurate pace data from satellites.

I use a chest strap, they’re all equally as good these days in my normal usages, and I use a footpod called STRYD for super-accurate pace and distance. Yet, like everyone else, I like to see a pretty picture of where I’ve been on my workouts and I like the GPS coordinates to be sent to STRAVA to get me one of those elusive KOM/QOMs on STRAVA. For my STRAVA data, I really don’t mind if I use GPS or GPS+GLONASS or GPS+GALILEO, sure it’s best to be as accurate as possible if you are interested in your segment performances but I’m not that precious about accuracy there.

We are all different when it comes to the accuracy we want and the accuracy we might possibly achieve. Some of you don’t like chest straps and some of you don’t want a footpod or DO want super-accuracy for your bike tracks on STRAVA. To generalise, I would say that GPS-only is the best AND it also uses less battery. GPS+GLONASS and GPS+GALILEO both have the potential to be more accurate but generally don’t deliver in my experience. Garmin keeps iterating GLONASS and GALILEO firmware but it’s simply not as good as GPS-only on the Polar V800 from 5 years ago – there are FEW, if any, knowledgeable people who would dispute that.

There are many varied and complex reasons behind GPS accuracy and now is not the place to discuss them. Let’s leave it with an honest acknowledgement from Polar that even the strap you use can affect GPS accuracy. #ItsComplicated

But you came here to see the accuracy of the Polar Vantage…I mean Grit X. 😉 Slip of the tongue. Let’s get on with it.

HR Accuracy

Bike HR is great indoors and variable outdoors with some quirks.

That one sentence just about summarises it all and these 4 charts give some more detail to back it up.

Here are two charts for running which are not great. The first shows where I was wearing the Polar quite a little too far from the wrist bone, as you can see this gives good HR results in steady-state exercise. Unfortunately, at some point, the watch becomes loose, slips down your wrist and rubbish data is produced. A similar thing happened to the Garmin on the other wrist, although you can see the Garmin starts to throw out a few poor peak readings much earlier. The second image shows something that has happened a few times where I get unusually high readings at the start from the Grit X.

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I might add some better running HR charts [here] but I tend to avoid using oHR for running as I am one of those people where it rarely gives good results, so I’m kinda wasting my time whereas you could quite well experience oHR perfection with the Grit X…or not. It depends on how and where you exercise as well as your physiology.

Elevation Accuracy

The Grit X has a GPS -augmented barometric altimeter that benefits from periodic, manual calibration at known altitudes. Polar told me that, during the first few minutes of your run/ride, GPS is used to check and set the altitude if it can.

As you can see the Grit X is good when compared to a ‘correct’ DEM elevation profile. The 945’s elevation doesn’t easily display in this software which is why it appears to be hidden.

GPS+Galileo Accuracy – Running

The Coros Vertix (GPS-only, red) compares badly to the GPS+Galileo tracks of both the Polar Grit X (Green) and Garmin 945 (Blue). This test was performed in typical suburban UK conditions, running fairly close to boundary walls, houses and trees. You can see that, at a high level, it simply doesn’t matter whether or not you have the Garmin or the Polar. If you zoom in to check every twist and turn then Garmin does win the majority of the GPS-tussles but Polar wins some too.

The Vantage never excelled with GPS+GLONASS, so I didn’t expect the Grit X to either and based on the very limited number of runs I’ve done with GLONASS in previous weeks, there’s nothing to change my mind. So, instead, I decided to do my formal test (and the majority of my run workouts) with GPS+GALILEO as I was surprised to find I hadn’t tested the Vantage formally with GALILEO. What did I expect? A: I expected that Galileo was relatively newly added to the Vantage and so wouldn’t yet be properly optimised for the Grit X.

I was wrong. The GPS+galileo was actually alright. Certainly, it’s OK at a high level and usually when looking even closer it was alright too. When I first glanced at the following formal test results I was quite excited and thought that we could be on for a great score. Sadly not! It’s still relatively good in a “meh” kinda way and matched a typically good Garmin performance. Grit X scored 77% and the highest Vantage once scored was 79% with Glonass which is the same as the best Garmin score on any Garmin device EVER. The following images show this formal test with the Coros having a relatively bad day (Glonass this time) and I’ve also overlain one of the best tracks from a couple of years ago with an Ambit 3 just to prove that better tracks are sometimes possible. Even then they are only slightly better.

What difference does it make? A: I guess it depends on what kind of accuracy you want.

If you were looking for accuracy of distance when recorded by GPS then, on the previous run, you would have been happy with the measured 16.700km which is a mere 100.34% over the likely true distance. That’s an error of less than half a per cent. Yet this really means that the under-estimates and over-estimates just happen to near-enough balance out. In demanding built-up areas you could still experience VERY significant variations to the true distance. The reason I also look at smaller-scale accuracy is that the accuracy at any given time will likely be reflected in the accuracy of the displayed running pace. It’s kinda handy to know how fast you are running at…no? No running watch in existence today can do that reliably accurately from GPS/GLONASS/GALILEO.

Unfortunately pretty much every device fails to some degree with instant pace once you start to deviate from straight lines with a clear sky. Polar Grit X was no different. It had good instant pace in good GPS conditions but I most noticed marked inaccuracies when making turns, it was generally ok under light tree cover on the occasions I looked. #FootpodBaby

GPS+Galileo Accuracy – Cycling

This time the Garmin is on GPS+Glonass and the Polar stays on GPS+Galileo. Wahoo joins the fray and should have an advantage being mounted on the handlebars.

Again, at the high-level everything is hunky-dory.

From that second ride, the Polar was the better of the 3 as Garmin still need to work on GPS+GLONASS. Though having said that Garmin (Green) did sometimes beat the Polar (Blue). The Wahoo seemed more consistent but unremarkable with the odd wobbly yet over the whole ride, Polar edged it IMHO. This level of accuracy is fine for me when cycling as I look at power data not speed. If you are going over 60kmh you should be looking at the road, not your watch.

GPS + Glonass Accuracy – Open Water

I have mostly done OWS with the Grit X using Galileo and it’s not great. However, switching over to GPS+GLONASS is fairly good. Here the Grit X is in red and not quite as good as the FR945 also using GLONASS yet both are more than acceptable compared to the OWS horror stories you are likely to get with other devices that do not have a properly optimised OWS GNSS profile.


The same setup again with the Grit X and FR945 both using GLONASS at Shepperton lake doing over 2k and 3 laps. With only two watches it’s not possible to say with certainty which one is right (it’s the FR945 😉 ). However, the Grit X (Blue) has two clear and unusually-shaped diversion to the right and to the top-left. So the FR945 is better than the Grit X but I’d say that Grit X track was good enough for me.


Again another comparison to the 945 and both with GLONASS. The FR945 (red) goes wrong toward the top RHS and the Grit X, even ignoring that error from the FR945, is probably slightly better here. This is Diver’s Cove (Godstone) again where the quarry has a higher bank and closeby trees that at other places I swim.


Finally, This was a post linking to my first couple of OWS swims with the Grit X in 2020 using GALILEO (ie the ones that aren’t so good)

Polar Grit X – First Swim (Accuracy)


Grit X Accuracy Summary

There are many competitors that are worse, some that are FAR worse and a select few that are sometimes better.

For OWS use GLONASS, for cycling it doesn’t really matter and for running those of you who aren’t too bothered about accuracy can use any of the options, maybe give Galileo a go. If you want running accuracy use a footpod and set the track recording to use as few satellite constellations as possible and save some battery life!



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