Elevation problem

UPDATE #8

Ride 129 is bad again. I did not used gadget.

Just after I did stop activity.

Yesterday calibration, today 

Same elevation on start and stop. I started outside and stoped on the 2 flor.

Gregor K. said:

Same elevation on start and stop. I started outside and stoped on the 2 flor.

how did you configure "watch mode"  of barometer? did you choose "auto" or "altimeter" or "barometer"?

No, I read you were using auto mode and that's what I'm referring too.  Your watch has no idea if you just ran on a hill slope or if a gust wind hit you.  It does nothing more than guesses when in auto mode as to what made the barometer change.  Sometimes it's right, sometimes wrong and sometimes it's way off.  For example, I was in Las Vegas in August when the ambient temperature was 109 degrees Fahrenheit and I was walking on the strip.  Any time I entered a casino that was air conditioned around 70 degrees, as soon as I walked a couple hundred feet my barometer changed and adjusted my elevation to crazy levels.  My elevation only changed maybe 10 feet, so I had to take my watch out of auto mode and set it to barometer mode to maintain correct elevation readings.

Hey. Auto mode

No, I read you were using auto mode and that's what I'm referring too.  Your watch has no idea if you just ran on a hill slope or if a gust wind hit you.  It does nothing more than guesses when in auto mode as to what made the barometer change.  Sometimes it's right, sometimes wrong and sometimes it's way off.

So you recommend to use altimeter mode? Are you using that on 945?

Why does garmin enable auto mode? They could do this as follows: automatically change the watch mode to an altimeter for a specific activity such as bike, walking, running ... and for other activities change watch mode to barometric mode. And they wouldn't have to bother with the automatic mode.

Yes, I use a 945.  

Why does garmin enable auto mode?

I leave my watch in auto mode the majority of the time.  Most of the time it works quite well.  Depending on the activity and the conditions, there are times I'll change the modes.  Most people aren't outside for awhile prior to starting their activity where the watch has had time to adjust to the change in pressure and temperature.  That's why I said it's important to note the pressure readings before, during and after the activity so these changes in elevation can be recognized.  I'm sure you've read many of the "I went on a run today, and my start and stop points had different elevations even though they were both the same spot" threads.  How many left a build or vehicle and then started their run soon after?  Did the watch already adjust to the new temperature or pressure change.  Did the wind pick up or start gusting?  I'll ask what their barometer read before, during and after their run and they'll have no idea nor wonder why it was important to do so.  Next time you do a test activity, pay particular attention to the readings.  Outside of a defective watch, you'll notice it does make sense what's going on.   

UPDATE #8

I did exchange 5 emails with [email protected]. Because I dont live in Englad they said that I should contact my local garmin support in my country, they did send me a contact, which I did already know. 

I did prepare document with description of problem. But before that I did try to phone them. My 3th attempt was successful and answer was:

1) accuracy of barometric altimeter is cca 20m

2) I have to calibrate altimeter before each ride

3) I have to use only altimeter watch mode (he said that I have to decide depend on activity, but for MTB in hills I have to use altimeter). His argument was that the weather is not changing so fast so assumption is that during the activity will be almost the same pressure. I did think about that and I did try to find how fast can pressure change (exclude situation that storm is coming). I did not find anything so I did check national weather station report. They have 7 day chart and max drop was cca 0.6hPa per hour. Lets say that pressure can drop 1hPa per hour, that means 10m diff. I think that I can accept that.

Conclusion: I decide that I will try my MTB ride with watch mode = altimeter.

@TMK17 mentioned that before activity we should be outside for awhile. Usually I am outside cca 10minutes out before I start to ride bike, checking bike, puting shoes on ... (garage is open) AND when I am cca 500m away from home I am starting activity. I am lucky, because in that distance from home I have tourist guide post with altitude information so I can calibrate altimeter. Maybe I will extend those 10minutes.

If problem remain, then I will send watch to garmin.

Yesterday I bought a Garmin Forerunner 945 and the sensor is also in the back, but the result after two activities, sweating a lot, has been perfect. In a cardio activity in the Gym the altimeter has not moved anything, in the instinct it was a roller coaster.

So I think it must be a hardware problem, and not the sensor position.