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Elevation calibration required?

I ran laps on a track yesterday (about 7 loops) and elevation should have been a repeating profile for every lap. But it was pretty terrible and all over the place.
I read something about elevation calibration in another topic here. How do I do it for the VA3?
Thanks.

0 jim_m_58 over 7 years ago

On the watch, go to Settings>Sensors>Altimeter>Calibrate

0 djwalker1260 over 7 years ago

The altimeter is set to "Autocalibate" by default. It sets the altimeter to the GPS altitude when GPS gets turned on. This corrects for temperature change, etc. For me this has worked well so far.

0 sigmoidx over 7 years ago

On the watch, go to Settings>Sensors>Altimeter>Calibrate

It allows me to enter an elevation here? Not really sure what I should do in this page?

0 FelipeSerra over 7 years ago

Today i've start a walk activity, altitude by Iphone was 600 meters, altitude registered by the vivoactive 3 was 300 meters, something is wrong, the setup was autocalibrate, now i turn it off and manual calibrate with the iphone elevation.

Something is wrong here.

Here is the activity, i'm in Santiago... 580 meters above sea level minimum.

https://connect.garmin.com/modern/activity/2246374252

0 the5krunner over 7 years ago

enter your elevation !!
there are sites like whatsmyelevation.com or similar

0 FelipeSerra over 7 years ago

Yes, i did that, but no the idea...

0 Former Member over 7 years ago

The altimeter is set to "Autocalibate" by default. It sets the altimeter to the GPS altitude when GPS gets turned on. This corrects for temperature change, etc. For me this has worked well so far.

That seems backwards considering I thought a major benefit of having a barometric altimeter is to avoid depending on GPS elevation .

0 FelipeSerra over 7 years ago

Elevation got stable readings, but since last update things go wrong, again. anybody?

0 AllanOlesen67 over 7 years ago

A barometric altimeter works by measuring the ambient pressure at your location and comparing it to a known ambient pressure at sea level. The difference between these two pressures is an indication of your altitude. At lower altitudes, 1 millibar of difference is roughly equal to 8-9 meter of altitude.

However, the ambient pressure at sea level is not constant. It changes all the time. Values between 980 millibars and 1030 millibars are quite common.

If 1 millibar is equal to 8-9 meter, and the pressure at sea level changes 50 millibar, the result is easy to imagine: The reading of the barometric altimeter will change by more than 400 meter, even though the altimeter has not moved.

So a barometric altimeter needs frequent calibration. Very frequent. The reading can easily drift 10 meter/hour with normal weather variations. That is not an error of the altimeter.

As to why one would prefer a barometric altimeter: The barometric altimeter will show the variations of altitude over short time much more accurately than a GPS altitude measurement will, even if the absolute measured altitude is wrong. So when you take a bicycle trip with lots of small climbs, for example 10 meter each, the accumulated ascent and descent will be much more accurate when you use a barometric altimeter. With a GPS altitude measurement, such small climbs may drown in GPS noise.