View Full Version : Fenix: inaccuracies in ascent/descent totals

09-17-2012, 01:03 PM
I was under the impression that the built in altimeter was supposed to provide a fairly reasonable estimate for elevation changes, however in practice that is not happening for me. On a 22ish mile run in the mountains yesterday the watch stated that I had climbed nearly 14,000ft (no significant change in weather during that time). However, based on topo maps I would have been surprised if it was over 5,000 ft in reality. When I uploaded the data to garmin connect and used the elevation correction it suggested around 4,500 ft of climbing which seems plausible at least. I've had similar results even on relatively short run around the city.

Is there something that needs to be done in ordering to get the alitmeter to function accurately or is this a software/hardware bug? Didn't see anything in the manual.

09-17-2012, 03:11 PM

What settings u have in: orange Key>setup>sensors>altimeter?

My settings are:

Autocal: On
Baro. Plot: fixed (I want to see weather changes)
Elev. plot: Elev / time

Maby u need to set autocal Off, and do a manual calibration?

09-17-2012, 05:05 PM
I have:

Autocal: On
Baro. Plot: Variable
Elev. Plot: Elev / time

Tomorrow I will try calibrating to a nearby benchmark and see how that works.

Do you know what would make such a manual calibration invalid, or how often I would have to recalibrate? I'm wondering if a change in weather would invalidate a manual calibration?

09-18-2012, 01:47 AM
I'm not sure about that, but i'll try to find that out for u. Maby if u go flying a manual calibration will become invalid since the cabin is pressurised.

09-19-2012, 08:44 AM

I got a simular issue. When I start the tracking the watch seems to start at 0 meter above sealevel. Then it jumps up to the current height leaving the difference as a result at -zero- seconds. Say I'm starting up the GPS at Current height 100m. The clock then states that I've climbed 100m before I even started. So I've turned off Auto start. Then I start up the GPS (Start GPS). Then I start the tracking and stop it again right afterwards. Then I delete the track. And THEN I start a new one.. This time the watch states that I am at 100m but I haven't climbed more than 0m (just as expected)

09-19-2012, 09:26 AM
That's definitely an issue. I have auto start off anyway and let it set the current elevation before starting the track and it seems to avoid that.

But I think the ascent/descent tracking issue is in addition to the start up issue. Yesterday I went for a 10 mile run where I started at about 300 ft above sea level and then went down to sea level where I stayed the rest of the time. Except for that first downhill segment the terrain was nearly flat. With elevation correction on garmin connect this route is usually 530 ft down and 250 ft up. However when I was done the fenix said 7,830 ft of ascent and 1,863 ft of descent. This is a _huge_ error!!

What I noticed at first was that every time I looked down at the fenix it seemed to have a reasonable reading for the current elevation so I thought it was working OK. Then I started to watch it more closely and noticed that it was actually continuously moving. If I ran for 30 seconds on a flat segment the elevation would fluctuate between 5 and 15 ft constantly. This constant movement was then being counted in the ascent and descent totals. Because of this I could run a downhill segment (that was clearly only down) and the watch would actually end up increasing the ascent total substantially.

It appears to me that this is a bug that garmin will hopefully fix. I don't know how much it has to do with the hardware, but an easy workaround would be to display a 5-10 second moving average for the elevation instead of a real time value. And then also use this moving average in calculating the ascent and descent totals. This would be akin to what is done to stabilize the "instant" pace readings from the gps measurements.

09-22-2012, 07:55 AM
It looks like Garmin fixed this issue with the firmware update (2.6.0) that was posted yesterday. Awesome!