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Altimeter Discussion

Former Member over 6 years ago

I have owned a Garmin 935 from almost when they 1st came out. Before the 935 I have a Fenix 3 HR, before that a Garmin 920XT and others before.

I really want to like the the 935, I love the size and weight of it, the battery life, the fit, the operating system and I like the idea of what its meant to do - I say idea of what its meant to do because I find it horribly unreliable. I have a spoken to Garmin support many times and I have even been sent a replacement watch and I have always been on top of updates, but I have no resided the fact that the watch is not very good by design.

Like everyone else I have massive problems with the Altimeter, every activity I record that is on land I get inaccurate information about altitude. My Altitude may start out correctly (I will often re-calibrate before an activity as its reading wrong), but the activity will always end with -36 or something like that. Why or why Garmin can my watch only use the Altimeter for Altitude? Your cheaper watches use GPS and I have found this far more accurate (my GF's watches she has had).

9 out of 10 sea swims I will get poor GPS data from, its usually very erratic, it usually looks like its only recorded half the distance or just draws dead straight or erratic lines. I have tried all satellite combinations but no luck. Sea swimming is probably the biggest failure of the watch. My GF's cheaper 735XT usually has no problems with sea swims.

Any running or cycling activities that might be over 4 hours - there will be a high chance of GPS failures here. GPS may drop signal for 5 - 10 minutes for no reason, in broad day light with no hills or trees in sight. I have also seen my GPS say i'm riding 100kms per hour when i'm stood still. Once again I have not seen these issues on my GFs 735XT. I have tried many different settings and satellite combinations but no good.

I have a few friends that own this watch but they don't see any issues, but they use their 935's for running and usually nothing longer than a couple hours.

So why dont I switch to a 735 you ask? Well I need the long capacity of the battery as many of my activities are long distance.

What do other people use and do that may have the same issues as me? Do you recommend other watches and what watches? The Fenix 3HR I felt too big on my wrist and caused me a bit of pain on my skinny wrists. I have heard the Fenix 5 has problems too, I dont know anything about the Fenix 5 Plus except its very expensive.

0 sdantasbvi over 6 years ago

Well, had my 935 changed by Garmin because of the altimeter and I am considering asking to have it changed again. was on the 3rd floor of a building today and Altimeter was showing -3m (I do live at sea level but was actually at least 12m higher!

Cheers,

Sergio

0 AllanOlesen67 over 6 years ago

was on the 3rd floor of a building today and Altimeter was showing -3m (I do live at sea level but was actually at least 12m higher!

When did you last do a calibration before that?

The pressure of the air around you can easily change 3 millibar over just 3 hours. This will give an altitude change of 25 meter. This has nothing to do with the watch.

So if you want accurate altitude, you need to do quite frequent calibrations, so the watch knows about the changes in the air pressure.

0 pasor1 over 6 years ago

I had my 935 change 3 times cause altimeter issues. If you can, do a simple test: disable altimeter autocalibration, take note of the initial height. Put your 935 in a place with a temperature at least 10° higher or lower... wait about 30 minutes... detected altitude should be constant. But in most cases the 935 detect a pressure change , resulting an altitude change.
My 935 works well intially well, then after a couple of month gradually get worse.
Here you can see a faulty altimeter: https://connect.garmin.com/modern/activity/2385354539 (note temperature and heigth charts)
Here the correct behaviour: https://connect.garmin.com/modern/activity/2444043719
In my opinion it's a bad design issue, or a low quality component issue.

0 Steph74-74 over 6 years ago

Pasor1 I made your test and I have the same behavior that your faulty exemple but reverse. In your test altitude increases with lower temperature. In my case Lost of 100m with 20° temperature drop and back again when temp increases

0 ekutter-dnu over 6 years ago

There are a couple different issues here. One is the wrong starting elevation, and that has to do with calibration. The only time I care about whether it is properly calibrated is if I'm in the mountains and know the tops of ridges or peaks. I want it to be accurate. Other than that, I really don't care if the entire graph is shifted by 50m up or down. The ascent/descent will still be accurate.

The 2nd issue is does it drift over time, and this is the bigger issue, in my opinion, as it impacts ascent. This is usually due to temperature changes or weather system changes. But in the mountains, where you really really care about this, chances are you will get swings in actual weather (temperature and pressure) that will greatly impact this.

I wish Garmin did a better job with continuous auto-calibration. I thought with the Fenix 5+ line, they were supposed to calibration based on topo maps but I haven't noticed it. Anybody know anything about this? Yes, GPS elevation can be off significantly, but with a good signal, I find it often is more reliable than barometric pressure. Especially in the mountains, GPS elevation tends to be much better as you are approaching a peak. GPS elevation's problem isn't so much that it is way off (usually it's within 30' in my experience), but rather it can swing quickly by measurable amounts (up 30', down 30', over seconds). So ascent is pretty much useless.

0 oBuTTuSo over 6 years ago

I had my 935 change 3 times cause altimeter issues. If you can, do a simple test: disable altimeter autocalibration, take note of the initial height. Put your 935 in a place with a temperature at least 10° higher or lower... wait about 30 minutes... detected altitude should be constant. But in most cases the 935 detect a pressure change , resulting an altitude change.
My 935 works well intially well, then after a couple of month gradually get worse.
Here you can see a faulty altimeter: https://connect.garmin.com/modern/activity/2385354539 (note temperature and heigth charts)
Here the correct behaviour: https://connect.garmin.com/modern/activity/2444043719
In my opinion it's a bad design issue, or a low quality component issue.

So, I did this test as well. Started an activity, took the watch off the wrist and placed it outside for a while to cool off, then put it back on again and wore it for some more minutes. I got elevation changes matching the temperature: https://connect.garmin.com/modern/activity/3307807472
But is this a hard or soft error? I mean the temperature sensor seems to be ok as it can record the temperature? Is it then the software that doesn't compensate for the temperature/pressure?

0 Former Member over 6 years ago

do a simple test: disable altimeter auto calibration,

I've locked my watch in "barometer" mode with my elevation calibrated to 470' so any pressure changes will be seen as temperature/weather changes and not elevation changes. The problem I found is as soon as I start an activity, my elevation will change as the pressure changes. Once I complete the activity, the watch locks the elevation (whatever the elevation measurement was following the activity) and goes back to "barometer" mode. I then have to calibrate my altitude again. So, regardless of what mode you're in, once an activity is started the watch defaults to "auto" mode until that activity is completed. The "auto" mode then guesses if the pressure change was due to actual elevation gain/loss or actual temperature/pressure changes. I don't know if going back to "auto" mode durning an activity is by design to record ascent/descent or if it's a software fault. This is what you and oBuTTuSo are seeing. Outside an activity, everything works correctly. Once I start an activity is when the elevation readings start to drift. Try this. Calibrate your elevation and then lock your watch in "barometer" mode. Note the elevation and pressure reading. Conduct the same test you did prior, but do so this timewithout starting an activity. You'll notice that even though your pressure readings have changed, the elevation will have stayed the same.

0 nradov over 6 years ago

The barometric altimeter can give screwy data at times, and I agree it would be nice if there was a way to disable it in favor of GNSS when you have a good satellite fix. But you can work around the problem after the fact in the Garmin Connect web application. Just enable the "Elev Corrections" option on each activity. That will correct the track to use accurate survey data.

0 runningfan97 over 6 years ago

What is the recommended setting for the altimeter? I have set it to Auto which should take GPS height and calibrate it, right? Barometer is set to Watch Mode (or whatever the translation is) to Automatic. Or is it better to put to Altimeter?

In my runs since around November I always get far too high readings in elevation. When looking at the elevation profile (I live in an almost flat area), the readings are far off in the first 15 minutes or so. It always starts at around double the height where I am.

0 Former Member over 6 years ago

What is the recommended setting for the altimeter? I have set it to Auto which should take GPS height and calibrate it, right? Barometer is set to Watch Mode (or whatever the translation is) to Automatic. Or is it better to put to Altimeter?

This is really personal preference depending on the weather or terrain where you're currently located. Here are the three barometer settings and what they do:

Different Barometer settings:

Auto (default setting): The watch will monitor changes and automatically switch between altimeter or barometer modes
Altimeter: The watch is locked in altimeter mode and all changes in pressure will impact the elevation reading
Barometer: The watch is locked in barometer mode and all changes in pressure will be considered due to weather and changes in ambient pressure

I live in the Pacific Northwest. I have the ocean to my west and the Cascade Mountain range to my east. My barometer is like a yo-yo because of the weather and terrain here. My residence is at 470' with slight elevation changes in my neighborhood so I keep my barometer mode to "barometer". This works great as my altitude remains at 470' and the pressure changes I see are considered due to weather. BUT, I have found as soon as I start an activity, the barometer mode defaults to "auto" and my elevation will change according to pressure changes. It will do so until I complete my activity and then it goes back into "barometer" mode. The issue here is once the activity is completed and it switches back to "barometer" mode, it locks the elevation that the watch had during the activity and doesn't revert back to 470'. I have to calibrate the watch again right after I complete my activity. If this isn't done and I continue with other activities, the elevation will be off and over time can drift by hundred's of feet. It's speculation on my part, but I believe the watch does this so it can record ascent/descent during the activity. I've done an extensive search, but I can't find any documentation on this. Garmin has always been a little vague when explaining functions of their products. Anyway, outside of people who are getting crazy altitude readings of + or - thousands of feet, I think this is what a lot of users (not everyone) are seeing and then are coming to the conclusion that their watch or software is defective.