I am having problems with my altimeter, its always on and it displays an inaccurate, i always re calibrate using the GPS.After a while it gives me a wrong reading again .I sometime get negative altitude levels..

The problem is that the air pressure around you is changing all the time. That is a simple property of weather.

Consequently you will need frequent recalibration of the altimeter. It is not an error of the watch. It is just how altimeters work.

Imagine that you are at altitude 50 meters on a day where the barometric pressure is 1010 millibar. You calibrate the altimeter to 50 meters. The next day the barometric pressure is 1020 millibar. The watch will see a pressure increase of 10 millibar, which equals 80-90 meter of descent.

So now the watch will have to guess if you actually descended 80-90 meter - which would place you at an altitude of -30 to -40 meter - or you stayed at the same location and the barometric pressure increased. The watch can't know for sure, so it will have to guess. Sometimes it will guess wrong. That is why you have to calibrate frequently.

Than you Allan ,i live at sea level in Mauritius .I travel extensively and experienced the same problem in paris,london,dubai,cape town ,johannesburg,Mumbai,Bristol,Southampton,Antananarivo,Toliara..and its still the same issue it just doesnt give me the correct altitude figure.It cant be that the air pressure is constantly changing in all these areas?am i the only one experiencing this problem ?

Right now the reading is 147 Meters and i am at sea level..btw my Garmin has the setting auto calibrate continuous ,so it should be accurate at all times from my understanding at least?

The record of my different activities are wrongly recorded , i sometime have negative starting point altitude.Not later than Tuesday on Garmin connect i had a starting point at - 158 meters and as fact i was At around 20 meters.

It cant be that the air pressure is constantly changing in all these areas?am i the only one experiencing this problem ?

Why would it not change in those areas?

I don't know of any area in the world, where the air pressure is not constantly changing. Look at the local weather station for your area. It will report barometric pressure. If you watch that number for a few months, you will probably see variations of +/- 30-40 millibar.

For a barometric altimeter near to sea level, each millibar is equal to 8-9 meter. So if you don't calibrate your altimeter to today's barometric pressure, it can be several hundred meters off.

Same if you travel. The barometric pressure is not increasing and decreasing simultaneously all over the earth. You can have high pressure at one location and low pressure at another location. So if you calibrate your altimeter at one location and then travel to another location, you should expect the altimeter to be off a lot.

As I said: Frequent calibration is necessary, and that is not an error. It is how weather works.

Regarding auto calibration:

The watch has different settings for auto calibration in activities and out of activities. Both need to be configured separately, and both have caveats:

The calibration out of activities runs once per night. It uses the phone to get a location, and then it finds the altitude for that location in the DEM map in the watch. A lot of people have experienced problem with this, often because of permission issues with the phone's location services. If it works, you will wake up with the correct altitude on the watch, but you should expect it to drift over the day as the weather changes.

The calibration in activities should not have this problem. But you should wait for green ring (full GPS fix) before you start the activity. Otherwise you can't be sure that you will get an auto calibration at the start of the activity. (And I don't know if a missing calibration at start will disable the continuous calibration during the activity. It would make a lot of sense if it did.)

In both cases, there is another caveat:
The watch don't know if you are at terrain level when it reads your altitude from the DEM maps. If you are in a very tall house while the watch is auto calibrated from DEM, the calibration will be wrong. So if terrain level is 10 meter above sea level, and you sleep 100 meter above terrain level, the nightly calibration will calibrate the watch to 10 meter. When you go out of the building at terrain level, the watch will now show -90 meter.

Hi Alan , i am not in air conditioned environment when checking the altitude reading on my Garmin , its mostly doing an activity.

Seriously - was the air condition side note all you managed to take away from all of this?

To me what's interesting is that usually my watch has the wrong altitude before an activity. Then I press start for running, wait for the green light, then start again for start the run. When I will finish the run, half hour later, and exactly on the same location I started, the watch will still give me a wrong altitude, and also far from wrong starting altitude. If I calibrate manually before the activity, everything is fine.

So, is the auto calibration working? Any insights on this?

Thanks.

ricardjs said:

and also far from wrong starting altitude.

I don't know what "far from wrong" means. Is that the same as "correct"?