Problems with Altimeter

What you are experiencing is considered excellent for a consumer grade barometric altimeter. If you calibrate your altimeter in your Settings > Sensors & Accessories menu and manually input your elevation, before all outdoor activities where you want your altimeter data as accurately as possible, you can be as close to +/- 50 feet but it is not uncommon to see +/- up to 400 feet.

On your Garmin Connect web account, you can always auto adjust your elevation on the far right side when you go into a specific activity. Your activity with then be directly impacted based on a physical elevation map for your GPS course recorded during that activity.

Does GPS come into play, yes. However, calibrating your altimeter is the key.

- Barometric Altimeter Accuracy of Compatible Outdoor Devices

Hi Chris, thanks for your reply.

*What* can be close to +-50 but also up to +-400 feet? The barometric altimeter?

To me those values are the typical GPS altitude accuracies. I reckoned I should be able to improve on those with an additional barometric altimeter?!

I was hoping that calibration would help, and I almost always calibrate the altimeter before a run.

So basically, even with a calibrated altimeter, I can end up about 100 meter below my starting point. Far worse than my experience with GPS alone. That might be the best consumer grade barometers have to offer, but then I don't really see the use for them?

To me, an outdoors watch should not have to rely on an online 'altitude correction service'. The default in Garmin Connect is even set to 'off', with a hint that this should not be necessary  for watches with a barometric altimeter!

I live in a mountainous place, the first Instinct had similar but not so big problems as you have. Solar is accurate for me, plus or minus 5 m maximum. Aren't you covering it with a sleeve? Humidity can do a lot. Or a clogged hole? You can still try the DEM function with GPS. Your variance is really big. When I climb on foot or by bike from 700 m above sea level to 1300 m above sea level, it is only units of meters maximum.

I too think your variance is too big. Taking into account that you start and end at exactly the same elevation the graphs you show indicate elevation trailing off by 50 meters within 45 minutes. I've went through some of my own activities and for most of my 'looped' activities the maximum difference between recorded elevation at the start and end times (same location) is approximately 5 meter per hour of activity (i.e., 2 hour activity may show a 10 meter difference).

Some things I would consider in your case (not as a solution, but to get insight):
- Temperature / weather difference between start and end of activity. If you always run at the same time of the day (morning) perhaps the ambient temperature increase during the activity time makes the watch think you're descending
- Measure the ambient atmospheric pressure at the start/end location for the duration of the run without actually moving (i.e., leave watch recording elevation at home - assuming start/end is home -  with GPS turned off).
- Compare recorded elevation graphs to actual elevation graphs generated from a topographic (DEM) map for this specific course.
- Attach watch somewhere where dirt/sweat is certainly not the culprit (backpack outside).

Thanks, it is comforting to hear that you are able to get +-5 meters.

Are you using 'calibrate during activity'? I have noticed, that this seems to cause a drift in all activities; this morning my indoor 'Cardio' training  (without GPS) had a similar profile to my runs, i.e. Steadily decreasing:

Possibly the indoor behavior is related, maybe not. 

With 'DEM function' you mean for calibrating the altimeter? I just set my altitude to 602m since it's known. Should I rather use a different calibration function?

If you know the exact altitude, calibrate manually. During the activity, the DEM adjusts the height frequently and automatically if you set it. But weird that it changes altitude during cardio, maybe a really wrong altimeter.

henzim said:

Are you using 'calibrate during activity'? I have noticed, that this seems to cause a drift in all activities;

I'd tell that the drift comes rather from the change of atmospheric pressure and/or from the change of the temperature. The auto-calibration would oppositely rather cause a sudden abrupt change of the altitude upon each calibration.

Thanks for your reply and your typical elevation deviation.

For my next run I will attach the watch somewhere away from sweat.

I'll report back. 

After my last reply, I more and more get the feeling that the altimeter part is off. The barometer has a smooth profile over the day, bur my altimeter has very hard jumps during indoor activities.

My last reply showed an image of a smooth elevation decrease during indoor activity, but in fact about 40% of my indoor training look like this:

All while the barometer remains smooth.

Ah, like I am usually seeing during indoor activities. But Auto-calibration uses gps right? 

henzim said:

But Auto-calibration uses gps right? 

GPS and I believe also the DEM (if enabled)