Garmin Forerunner 945 – GPS Accuracy – GLONASS, GALILEO and GNSS Functions

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Garmin 945 (Yellow)

This is part of my main Garmin 945 Review and specifically looks at many aspects of GPS accuracy or, more correctly, GNSS accuracy.

I’m looking at FITNESS FOR PURPOSE but what purpose do you want a GPS track for? If it’s a pretty post-run or post-ride/run track of where you’ve been that’s ‘about right’ then most sports watches will be fine for you. If you want to use GPS to determine your walking and cycling speed then you’ll probably be alright too. It’s just that when you are running GPS has a tricky job of dealing with the environment and your swinging arm to give you a correct pace and distance. Most sports devices are not fit for the purpose of giving instant pace but maybe alright with your current lap pace. Think about it….a running watch can’t really tell you how fast you are running. Hmmm.

They probably also misestimate distance by 0.5% or more in tricky, urban conditions.

I’m also looking at the accuracy of using the American GPS satellites and a little bit at augmenting that with the potentially superior European GALILEO satellites and we’ll leave the Russian’s GLONASS system out of it. There are other regional satellite systems too.

I’ve completed 2.5x 10 mile runs on my standard GPS course and following a set methodology with my normal usage in running and other sports. That means you can compare the 945 with the best GPS watches from yesteryear which most of you will know as the Polar V800 and Suunto AMBIT 3.

Note: I’ve only had 2 OW swims so far. One had an elemnt of ‘user error’ to contend with 😉 I’ll update that section in June probably (ping me below in the comments if I haven’t done that)

FYI: Garmin also uses the accelerometer in the watch as an input to their pace/distance algorithms.

GPS Accuracy – GLONASS, GALILEO and GNSS Functions

It seems that the new Sony GNSS chips used by Garmin from 2019 onwards can only use the E1 frequency (Galileo) and the L1 frequency (GPS). My understanding is that the accuracy of Galileo with a single frequency is similar to the accuracy of GPS with a single frequency. Thus you can only expect to get +/-5m accuracy BUT enabling GALILEO increases the number of visible satellites and hence GALILEO increases the probability of +/-5m accuracy being achieved.

The massive improvement in GNSS accuracy is most likely to come from dual-frequency Galileo (frequency E1 and frequency E5a). Put simply, if you run down the middle of the road today with your 945 then it’s perfectly acceptable for the watch to say you are running on the pavement on either side – that’s true of EVERY OTHER sports watch.

Credit: @Mirko, and others

Of course, the reality of any given situation is more nuanced and complicated than simply what piece of tech is on your wrist…try this link to see what else can go wrong.

As of 23 May 2019 my recommendation for you is to just use GPS but consider enabling GALILEO+hope where there are tall buildings and trees. @DCR notes that Garmin’s focus appears to be GALILEO right now, which is a roundabout admission from Garmin that it doesn’t currently work as well as it should.

It’s UNLIKELY that the 945’s current GNSS technology will ever deliver accuracy & precision in larger cities from a satellite signal alone. Buy a footpod like STRYD if you want more accurate running pace and distance measurement

I would contend that: GPS+GALILEO generally seems to make no overall difference or perhaps some slight, positive difference – but then sometimes it’s notably off.


Fiest up is cycling in the suburbs.

This was generally fine and I’ll highlight some exceptions. Here the 945 gets a nice track through the tunnel where there is no satellite reception (!) but to the left, it is too inaccurate, straying 10m from the true location.

945+GALILEO (Green), Edge 530 (red), Bryton Aero 60 (Blue)

In more open conditions or near these low houses (right of image) the 945 is good. However, on the left and nearer to larger buildings, the 945 soon becomes more than 5m inaccurate like the other 2 devices.

945+GALILEO (Green), Edge 530 (red), Bryton Aero 60 (Blue)

Around some low trees and at low speed the 945 is good

945+GALILEO (Green), Edge 530 (red), Bryton Aero 60 (Blue)

Although these navigations around a circle/roundabout look bad, I guess all are just about in an acceptable 5m off from where I really was…

945+GALILEO (Green), Edge 530 (red), Bryton Aero 60 (Blue)

Same here

945+GALILEO (Green), Edge 530 (red), Bryton Aero 60 (Blue)

Neither the 945 nor the Bryton are that great here in relatively benign conditions

945+GALILEO (Green), Edge 530 (red), Bryton Aero 60 (Blue)


Summary Cycling with GPS+GALILEO – it looks alright. It could/should be a bit better. I don’t have too many data points and am quite happy if others say they have better results. It seems pointless me doing too much with Galileo, as dcr says, Garmin are doing most of their tinkering with Galileo so whatever I find will soon be superceded by new Garmin firmware

Next up we have some GPS+Galileo-based running in the park

Here it’s not too bad and you can see that some nearby trees throw the Forerunner 245 off-course, whilst the 945 gives the smoother of the other two tracks – compared to the budget Ticwatch S2.

945 (Red), 245 (Blue), Ticwatch S2 (Green)

Then, later, this is pretty good in easy conditions (245 is not good)

945 (Red), 245 (Blue), Ticwatch S2 (Green)

And this is pretty good in easy conditions on  part of the Bushy Park parkrun course

945 (Red), 245 (Blue), Ticwatch S2 (Green)

With some trees and slightly taller buildings, we get this not-so-great performance from each watch. Very strange.

945 (Red), 245 (Blue), Ticwatch S2 (Green)

Yet on a different day in similar conditions, different results were obtained and the 945 was quite good.

945 (Yellow), Instinct (Pink), Coros Vertix (Red), TicWatch S2 (Green)

I put the 945+GALILEO through my formal test, albeit on the wrong arm (so the results don’t count) and it performed with a score of 69%. Compare this to the 935 which got 71% (MediaTek chip+GALILEO). Yet the 935 scored higher with GPS+GLONASS (79%+73%) and GPS-only (73%).

Summary Running  with GPS+GALILEO – it seems passable. Generally in good conditions the results are good enough, it’s just that GPS+GALILEO handles tricky reception conditions variably – sometimes good and sometimes not-so-good. I don’t have too many data points and am quite happy if others say they have better results. It seems pointless me doing too much with Galileo, as dcr says, Garmin are doing most of their tinkering with Galileo so whatever I find will change soon.

GPS- Only Accuracy

My testing with GPS-only has been more extensive with well over a few hundred miles of testing. I’ll do more over time and add bits in here as needed as the 945 will probably be one of my main ‘reference watches’ and so will be used quite a lot.

First to Riding

This was on a ride to Brighton on Ditchling Beacon which, despite awesome scenery, is one of South England’s more unpleasant rides when going uphill. The Bryton strayed a bit here under the trees on a gently winding road but both the 530 and 945 were good.

945 (Red), Edge 530 (Green), Bryton 60 (Blue)

Then on to one of South England’s more pleasant and famous cycling hills, Box Hill. A very pleasantly smooth road to put the power down on for a few minutes. The Bryton struggled here quite a bit and the 530 struggled as well to find the road. The 945 was not perfect but certainly ‘quite good’ (ignore the funny circles at the top of the hill, I was waiting for someone)

945 (Red), Edge 530 (Green), Bryton 60 (Blue)

Yet on a different day, there are different results even though the devices are the same. The Bryton was still off-track and, whilst the other two were generally good, it was the 945 that this time strayed 10m from the road (top, centre of image)

530 (Red), 945 (Green), Bryton 60 (Blue)

From the delights of Virginia Water in the previous image and, earlier, two of Englands pretty hills we move to Shepperton High Street, not too far from the OW swimming mini-mecca of Shepperton Lake. The Edge 530 is pretty solid here but the 945 drifts at the bottom, although to be fair it’s probably just about 5m from where it should be.

530 (Red), 945 (Blue), Bryton 60 (Green)

Running with GPS

Off to a flying start as I pass the Pheasantry Cafe in Bushy Park. I would have popped in for a coffee but the 945 was metaphorically on fire, putting down a good track under some trees. For a novelty, I even tried the 530 as a hand-held (blue)

945 (Red), handheld-53 (blue), 245 (Green)


I might use this bridge over a train line a little more as it seems to stress some devices even when there are clear skies. Here the 945 did well and the 245, errr, didn’t.

945 (Red), handheld-53 (blue), 245 (Green)

Then for some hill reps in Richmond Park close to where, today, Olympian Stuart Hayes was knocked off his bike by a deer. It all happens where I live (and best wishes to super-nice-guy Stuart for a speedy recovery). This image is still at quite a high level and all the 3 devices have moments of madness as well as moments of glory. the 245 was noticeably the worst and I ‘d say the 945 was reasonable-to-good in these fairly challenging conditions.

Then, just when you thought you knew how to predict the performances, you get this where the 245 nails a fairly hard section with very high brick walls and tree cover and the 945 wants to go swimming.

245 (Blue), 945 (Red)

Further on, in the same run, the 245 again nails a hard looped section under a bridge whereas the 945 doesn’t look so good but actually performs reasonably well if the difficulty is taken into account and if the tendency for ‘going for a swim’ ignored. #Sigh

245 (Blue), 945 (Red)

Finally, my proper running test with the 945 returned an ‘incomplete‘. The watch froze after about 11km (second time ever with a watch on the test). The test is physically non-trivial for me to fit in with my training so it is back in the queue for the 945. Luckily for the 945 it will probably get a few more re-tests as well and I will probably focus those on GPS+GALILEO for reasons outlined earlier (ie as Garmin improve the algorithm)

Open Water – GPS

To be added June 2019

Running Pace – GPS

It’s easy enough for anyone to wear a spare watch, go for a run and then look at the maps afterwards. I try to ‘test’ one watch at a time and do endeavour to use it to periodically check my instant running pace – in fact, just as you would do if it were you only watch 😉

The accelerometer/algorithms on the 945*DO* seem to give a generally good and stable instant pace when running in reasonably straight lines and in reasonably good ‘open sky’ conditions. But at other times there are notable discrepancies of 20-30 secs/km at any one time.


This is a mode that has nothing to do with accuracy and everything to do with battery-saving. The 945 has a great battery life and 99.5% of you will never need this mode. If you use it by accident it will give a ‘vague impression’ of roughly where you have been and you wouldn’t really have any idea of the exact route you took unless there was only one possible path within, say, 50m.

It’s only JUST better than nothing, IMHO.


945 – In Stock

Despite quite a lot of time with the 945, I don’t feel in a position to more definitive that GPS is better than GPS+GLONASS but that would be where I ‘d place a bet right now.

As of 3Jul2019 I would now say that the GPS-only performance on the 945 is on par with the 935. ie quite good but not excellent.

I understand that Garmin ARE STILL WORKING TO improve 945+GALILEO accuracy but I do NOT expect it will be a massive improvement and I DO NOT think it will end up being as good as the GPS-only V800/AMBIT3. Let’s wait and see…I hope I’m wrong.

Once again the sad, tentative conclusion is that if you want a pretty picture of where you are going then all is good. If you want accurate running paces and accurate distances then you need a footpod. I think I’ve said that before, somewhere.

Return to the main Garmin 945 Review



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