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920XT jumping all over the place

I recently bought a new Garmin 920 (have had a 310 and 910 in the past). I've run numerous times since my first run with it last Tuesday, but on the last three runs (commute to work yesterday, commute home and lunchtime run today) it's been highly inaccurate jumping 50-100m away and back over a few seconds giving incorrect pace, distance and traces. I ran today with another guy who has a 920 and his distance was significantly shorter than mine.

I did a long run on Sunday (36k) and it was fine.

Any suggestions?

https://connect.garmin.com/modern/activity/1013240493
https://connect.garmin.com/modern/activity/1013240486
https://connect.garmin.com/modern/activity/1013240485

https://connect.garmin.com/modern/activity/1011148651

Wil

PS: Also used it as a logger and it has jumped around as well since yesterday.

0 idelve over 9 years ago

Pictures attached. Screen shots as jpgs. Points represent 1 second trace points from FIT file.

0 idelve over 9 years ago

I just updated the software from 5.20 to 6.20 and the GPS software from 2.90 to 3.00. And turned off Glosnas. Hope this helps.
If not I'll try turning the device off before each Activity.

Any other suggestions still welcome. It just loses the plot every now and again, then recovers (either completely or with a linear shift, ie constant error or one that tapers back to the correct location).

0 idelve over 9 years ago

14 times

[lost post due to timeout].

Bottom line: Happened 14 times on a walk to a meeting and back last night (https://connect.garmin.com/modern/activity/1013452326), all to the left and some major.

I powered it off, waited 10 minutes and then powered it on before driving home logging the drive. It made it 90% of the way before jumping to the left (http://bd4.amristar.com/downloads/drivingExample.jpg). The new (9 days old) device was clean, dry and on my wrist. You can see from the picture (green dots every second) that it suddenly loses the plot (to the left) before correcting, getting back "more or less" onto the road.

Is this a fault with my unit? Looking back I see it happening on most activities. I only noticed it due to a sudden change in my lap pace (and distance seemed to be too high) while jogging home on Tuesday.

Wil

PS: Attached walking example picture. Heading SW through park when it suddenly jumps adding about 500m to the activity. http://bd4.amristar.com/downloads/walkingExample.jpg
It returns to the path through the park.

0 idelve over 9 years ago

More info. Happened last week (first week of ownership).

Looking back it appears to have happened last week as well. On one occasion I ran with someone else also using a 920XT and also on Garmin Connect. The two traces match well enough, but mine has a few minor and a couple of major spikes. There are a few other places of patchy reception (to be expected in places under trees) but other than that they all jump to the left and then come back over the next 10-20 seconds (getting back on track with a little more error).

Trace (made public): https://connect.garmin.com/modern/activity/1011151804
Friend's trace: https://connect.garmin.com/modern/activity/1007324909

http://bd4.amristar.com/downloads/kp1.jpg (significant, heading from top of screen)
http://bd4.amristar.com/downloads/kp2.jpg (minor, heading from from top)
http://bd4.amristar.com/downloads/kp3.jpg (major, heading from bottom) Major, but only added 100m of distance.
http://bd4.amristar.com/downloads/kp4.jpg (minor) Could be because of (single or low double story building to the left).

kp3.jpg occurred on the top/side of a hill/slope in and area that is very clear and should get good GPS signal (subject to clouds, satellite locations).

It's really starting to look like a fault with the unit.

Wil
--
My notes:
very minor at start.
minor 1.5k in.
very minor at war memorial
well defined one at Synergy Parklands (kp1)
little one approaching UWA (kp2)
Big one to the left in SW. (kp3)
Little on toilets, up hill.
Very little one crossing middle road heading north.
After Dave's work. (kp4)
Minor one 300m on.

0 idelve over 9 years ago

0 gerhardo over 9 years ago

You can add my investigation to your links:
https://forums.garmin.com/showthread.php?338848-High-variance-for-distances-for-920XT

My conclusion: GPS is significantly worse than older devices, much higher variance for results. The SW compensates quite well in good situations, but as a consequence it cuts corners considerably.

Response from moderators: I have too high expectations on the 920XT, the 920XT may be much worse than old devices like the 305.

The 920XT has a premium price but a poor GPS.

0 idelve over 9 years ago

Disappointed

Well, I'm happy that it "seems to have sorted itself out" but very disappointed that noone from Garmin has responded.

What I now think "may" have happened:
- I got the device, went crazy making profiles and used it for EVERYTHING including driving out to the bush, etc.
- Some profiles were "derived" from running but then I used this profile for driving at up 100km/h.
- The 920 modeled "stuff". Who knows, GPS locations, wifi strengths... perhaps internally to profiles.
- Even with upgraded firmware I had the issue... but it soon "faded" away.

What I've changed:
- I have not created any new profiles.
- I mostly power off the device and then re power it on before a run or on foot activity (leaving it so it can pick up a signal while still).
- If I do log an adventure or off road drive (or any drive) I use bike mode.

So, maybe:
- The internal stats are in better shape, hence it does not predict sudden movements like it did.

Who knows. But it has not happened since Friday the 15th.

What has happened:
- It has good traces. Better/same/worse than the 910/310. Hard to tell, but definitely not considerably worse.
- It does read "shorter" than the 910. Guessing software. Probably something like 0.5%, so 5m per km. I think I was getting something like 40-50m for a 10k run. That's fine. It's all an estimate. In fact I'm happy because this is consistent with other users.
- Wearing the 910 on one arm and 920 on the other... neither trace is clearly worse (they are just slightly different).
- I am beginning to trust the 920. I'm run 4 times since Wednesday afternoon (1 hour commute home (11k), two shuffles next to my 7 year old to school and back (2x4k) and a 1 hour commute in this morning) without another GPS or phone logging and without checking to see if the traces had issues. Just did now. No issues.

So, hopefully a software/teething thing. Or a strange usage thing. I wouldn't be surprised if some tech person saw this post and went "yeah, I figured that might happen... it will sort itself out" and let it slide.

0 JSRUNNER_ over 9 years ago

I had similar issues with my 920 which seemed to get worse after upgrading to 6.20 - also had a problem with it acquiring satellites before start of run then losing them and not regaining so recording distance off HRM run - Amazon replaced the watch (about 5months old) the new one I've had about 2 weeks and seems so far to be more reliable.

In all the above cases these are routes which don't have difficult satellite reception and on the occasions that I ran with my 610 at the same time the 610 recorded a reasonably accurate track.