I was looking at Garmin's product support page for the 935. While reading about elevation, the website explained the "auto", "altimeter" and "barometer" mode settings in quite detail. In the section about calibrating the altimeter it reads "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." Calibrating it manually with a known elevation or using GPS are self explanatory, but I can't find any info on auto calibration. Would anyone be able to explain what the auto calibration "on" does and how it does it? Secondly, why is there an option to turn it off? Is there a situation where one would want it on as opposed to off or vise versa? Any help with this would be appreciated.
I have described a method which will work on most Garmin watches with a barometer, and which you could try instead of your Saved Location method: Get a GPS fix, calibrate your altimeter manually. Then the watch will remember that location/altitude combination and use that altitude every time you start a GPS-based activity from that location.
Ahh ok I see it now. I read your long post about calibration and I actually just have to leave my 935 at auto, but then at start, recalibrate to known altitude, and the 935 will automatically adjust the next time. It actually works the same way, as with a saved location, with the Edge computers. I just never got that part understood right untill I read your explenation.
I started a run from my saved location and sure enough it was showing my altitude at 470' in my data field without any calibration, but it was showing 470' in the data field for the activity only. For everything else the watch was still showing 499'. Maybe I misunderstood, but I thought you were saying the watch will use this altitude to calibrate the altimeter?
Yes, it does. But only if you press "Start" in the activity after the watch has "locked on" to the memorized altitude. If you do not press Start and instead closes the activity app, the watch will forget everything and go back to its previous calibration.
After finishing the activity, you will see that the altitude widget has also been calibrated.
But then what happens inbetween? Will you see the new calibration in the altitude widget while the activity is still running? To be honest, I have never tested. I always make custom data screens for all the info I might need during an activity so I don't have to switch back to normal watch function in the middle of an activity. So I really don't know what happens to the altimeter widget. It may very well be using the old calibration until you stop and leave the activity. Someone pointed out some weeks ago that the barometer seems to have such a behaviour, so it is quite likely that the altimeter does the same since they are calibrated together.
Nope! I think my watch may be faulty. Tried again today. Alt at 431' before activity. Started activity and data field elevation shows 470'. Saved activity and it shows it was performed at 470'. All widgets I have on my watch that display elevation are still showing 431. My watch is still under warranty, so I think I may exchange it.
Update: So, I decided to try this one more time. My altimeter was reading 452' after my run this evening. I went to my saved start point and went to start a 2nd run activity. This time the data field elevation was still reading 452'. I thought maybe the GPS was off and it had me somewhere other than my saved location. I checked my saved location (my only save location) and it was there with an elevation of 470'. I hit navigate to saved location. It had me 23' west of the saved location. I moved 23' west and I started the run activity again. I don't know why, but the elevation was still reading 452' in the data field. So, within a couple of hrs I went from bad to worse. I have no idea where to begin to try and fix this.
Nope! I think my watch may be faulty. Tried again today. Alt at 431' before activity. Started activity and data field elevation shows 470'. Saved activity and it shows it was performed at 470'. All widgets I have on my watch that display elevation are still showing 431. My watch is still under warranty, so I think I may exchange it.
This would be a software error, not a hardware error. You can't fix a software error by replacing the watch with an identical model running the same firmware version.
Do you by any chance have the watch in forced Barometer Mode? I don't know how this would affect the behaviour, but it could be worth setting it in Auto or Altimeter Mode.
The auto-calibration or manual calibration at start is useless if your activity is in the mountains. After 30 minutes of climbing the barometric altimeter is 30-40 meters lower than real elevation. On a 8-12 hours activity the altimeter is way off even the weather is the same all day long. On the mountains activities (trail running, hiking) i use a 2 data fileds page with Elevation (Baro) and GPS Elevation. Always on the mountains the GPS Elevation is correct, and the Elevation is lower.
Garmin shoud include a auto-calibration with GPS at a specified time during an activity, like Suunto does. The previous Ambit 3 Peak always shows the correct altitude with "fused alti" (auto-calibrate) function active.
I'm finding that my FR935 has been showing gradually increasing elevations over time. I'm at ~5300 feet altitude but at one point my watch (at the same location) was showing well over 6,000 feet elevation. My watch is set to Auto, but I did do a manual calibration w/ GPS about a month ago (back to Auto afterwards). After that, the elevation has subsequently been increasing again on average about 100 feet a week (always up not down). I understand and accept that the elevation shown by the watch will vary over time due to pressure changes, etc., and I'm not that concerned about having a 'precise' elevation, but it seems odd to have to do a manual calibration every month or so to return the watch to an expected value.
I still think something is wrong with my auto calibrate on setting. So, I did a restore of my watch on the 9th. Started a GPS activity and manually calibrated the watch. On the 10th and 11th I started GPS activities at the same location and all worked well. The altimeter calibrated to the elevation set on the 9th. Yesterday and today I started GPS activities at the same location and auto calibrate did not work. It kept me at the altitude my watch was reading due to pressure change. Is it possible that the file that held the info from the 9th was overwritten? I wouldn't think 4 days of data would be enough to do so. Is it possible that the GPS fix for yesterday and today was so far off that the watch didn't recognize that I was at my usual starting point? I guess I'll just have to manually calibrate every activity until I can figure out what's going on.
I get tired of reading this. Sorry. People need to learn that air pressure can change, also when the weather doesn't change.
I know that. That's why i said that auto-calibration is useless. It doesn't help me to know the correct elevation at the start of the activity at the base of the mountain if it's way off after a few hours. They should implement a auto-calibration at one hour like Suunto.
