Altimeter/Elevation issue

Search before you post - https://forums.garmin.com/forum/into-sports/running/forerunner-935-aa/1312950-elevation-and-temperature-data-is-screwed-on-935-following-update-to-version-8-0-0

Search before you post - https://forums.garmin.com/forum/into-sports/running/forerunner-935-aa/1312950-elevation-and-temperature-data-is-screwed-on-935-following-update-to-version-8-0-0

In (the first posts/pages of) the thread people complain about completely wrong elevation values. This is not my case, even if the values could be more correct.
Therefore I added this one.

Just wondering if somebody noticed the same behavior.

BTW: I'm trying to sell my 935 on some online platform. If this problem should be corrected, I could decide to keep it.
...and no, It doesn't deliver 500$ more value that my old ambit 2.

No, I don't see this behavior at all. My office is on the second floor and if I have it on the altimeter screen I can watch my elevation change as I go up/down the stairs. Do you see this behavior only in an app/ during an activity? Can you see an elevation change looking at the altimeter widget and going up/down stairs? I would suggest clearing out a bunch of the old files from the watch, power off/power on, and then try updating to the beta software. Any of those might fix the issue you are seeing, but it is not the way the watch is supposed to be working.

In general my watch works perfectly. But I have also seen something similar to this issue, very occasionally. This is what I notice…
Suppose I have to do a manual calibration of my altitude because of drift over a matter of days or weeks. The new altitude value that I have entered in doesn’t come into effect immediately . But over a matter of three or four minutes the altitude slowly changes to the value that I have manually put in. Again, I can say that this has only been noticed by me perhaps six or seven times over the course of the last six months. Normally it’s fine.

Hi. I have similar experience with my fenix 5x.
https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-5x/1326484-altimeter-is-wrong-on-fast-decent.

nothing wrong when I am running.

For ski touring and hiking I have a screen on which I show current altitude and elevation gain. Since 8.0.0 the elevation gain sometimes lacks behind the actual altitude. While the altitude counts steady every meter by meter, sometimes the elevation gain remains frozen and then suddenly catches up by adding 30-40 meters (in a time frame of a 2-4 minutes). Eventually, the overall gain matches the elevation and also the track gets recorded correctly. It's just odd that during the activity this happens sometimes.

I got the following from Garmin support:

Incorrect Elevation or Barometer Readings on the Forerunner 935


If you experience incorrect readings from the altimeter or barometer sensors on your device, there are a few factors to consider that might be impacting these readings as well as some steps that can help increase their accuracy.

It's important to first understand how each sensor works:

The barometric altimeter on the Forerunner 935 uses barometric pressure to determine changes in elevation as well as pressure changes caused by weather patterns. Taking advantage of the fact that weather pressure changes occur at a slower rate than a person going up or down a hill, the unit will automatically transition between two modes; Altimeter or Barometer.

• Altimeter mode locks the barometer value and assumes all pressure changes are due to elevation change
  
• Barometer mode locks the altimeter value and assumes all pressure changes are due to weather
  

The device will monitor barometric pressure to determine which of these modes is most appropriate at any given time. When the rate of change in pressure is significant, it indicates movement and therefore the changes in pressure indicate elevation change. The watch will go into the altimeter mode allowing the altitude to change and locking the barometric pressure.

When the rate of change in pressure is not significant, it indicates no movement and therefore pressure changes are due to weather. The watch will go into the barometer mode allowing the pressure reading to change and locking the altitude.

Manually selecting a mode:

It is possible to manually lock the watch into the Altimeter mode if your activity involves changes in elevation or lock it into the Barometer mode if your activity is in a relatively flat area. The Barometer mode is also useful if you are more interested in your watch notifying you of impending weather changes instead of elevation changes.

The Barometer has three 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
  

To change the Barometer settings::

• Hold UP to open the main menu
  
• Select Settings
  
• Select Sensors & Accessories
  
• Select Barometer
  
• Select Watch Mode
  

Calibrating the altimeter:

To maintain accurate readings when using the altimeter/barometer the sensor needs to be periodically calibrated. By default, the watch will calibrate automatically using the GPS elevation reading whenever a new activity is started. However, depending on the GPS signal strength, these elevations can be off by as much as +/- 400 feet.

The sensor can also be calibrated manually, providing an accuracy of within +/- 50 feet. To maintain this level of accuracy the watch will need to be periodically re-calibrated over time.

To access the calibration options:

• Hold UP to open the main menu
  
• Select Settings
  
• Select Sensors & Accessories
  
• Select Altimeter
  

From here you can choose Calibrate to calibrate the sensor using a current known elevation or by using the GPS elevation reading, or toggle the Auto Calibrate setting on or off.


Other factors to consider:

Some factors that might impact the function of the altimeter/barometer might include rapidly moving air entering the sensor ports while participating in high speed activities; climate controlled buildings which can have slightly different pressure indoors compared to the ambient pressure outside; and soap, dirt, or salts from sweat which can clog the sensor ports. For the latter, you can try to clean the ports by soaking the watch in warm water with a little mild detergent.

Note: Never insert anything into the openings as it could damage the sensor insid

thanks kitenski for you input.

Actually, my 935 was set to "auto". I will move it to "altimeter" and retry. Unfortunately next week only...

Another note/clarification from Garmin tech support: I'd had an issue with gradually increasing reported elevation over multiple days (over 1000 feet in two weeks or so, from a base elevation of ~5300 feet) despite having the 935 set to auto calibrate. It appears that it's necessary to get a GPS fix before actually starting an activity (I had just been starting the activity without waiting for the GPS fix). Since I've been doing that, my reported elevations have been much more reasonable/accurate. YMMV.

Ok, I'm back.
Set the barometer mode to "Altimeter", here the result: https://connect.garmin.com/modern/activity/2723756617

As you can see, at the end for the activity there still are ~120m difference with the actual start elevation. And at minute 50 (during descent) I made 2' stop, where the elevation continued to decrease.

Useless.