total ascent measurement is very inaccurate

The first graph doesn't look normal. Looks like there's an issue with the pressure sensor in your watch.

Thanks for the answer!

Yeah, I also fear this. Anyway I've written to the support now, let's see how it goes.

I see nothing really unusual on the graph using the barometric altimeter. The pressure sensor is just sensitive to wind gusts or rapid air flow, which then triggers higher pressure reading (hence a brief drop of altitude). It may get even worse if moisture or dirt enter the port hole. Protect the sensor port (on right side) with a sleeve, sweat wristband, or a piece of textile, and I bet the reading will improve.

Thanks, I will do some tests this weekend.

I got my Instinct 2 a couple of months ago and have done about 20 hilly rides (~1000m 2 hour rides) using my Instinct as a backup and to see how it performed. I compared with my Wahoo Elemnt2 and Garmin Edge 500 (both excellent devices for total ascent rides).

I wore the Instinct on my left and right wrist with and without gloves, on my handle bars and also in my rear pocket and found absolutely no difference in performance with the alleged Gamin wind effect.

The good news is that my Instinct barometer records accurate and consistent altitudes and matches the Wahoo and Edge 500 meter for metre.

When on a climb, I.e. past the first bit of the transition to the hill, the instinct records all meters climbed again matching the other 2 devices.

However, the Instinct records 10% - 20% overall total ascent for every ride. This varies throughout the ride which further explains what is going on here. The Instinct accurately records meters but throws 10-20% away on the small 1 to 4m road bumps.  I see this on the very first little get out of the saddle hill which is 5m high and the Instinct records it as 3-4m even though the altitude has increased by 5m.

IMHO, this is over aggressive hysteresis in the Garmin total ascent algorithm.

i have also seen the same behaviour on hilly walks I know well shame really otherwise the Instinct 2 is an impressive bit of kit.

7780811 said:

IMHO, this is over aggressive hysteresis in the Garmin total ascent algorithm.

It may not be a problem of the hysteresis, but perhaps of the sampling rate. Do you use the default "Smart Recording", or the "1s recording"? The "1s recording" should give a finer resolution, and hence ignoring small bumps less. Still, if you go through the peak of the bump fast, a bit of it may go unaccounted for anyway.

My Instinct is set to record every second.  While it may be possible to hit a 1m hump back bridge at a speed high enough so that the device misses it, as I don't ride over any such bridges on any of my routes, and my rides fail to capture 100m to 200m, that cannot be the explanation.

My Fenix 5 did exactly the same thing and that was one of the reasons why I returned it.

Hello! I've done some tests recently, I placed the watch on the bike handlebar with some plastic adapter, and also on my wrist with special care to avoid obstructing the sensor holes with my hand (I tightened a bit less the belt and used a bracelet as distancer from the hand).

And I have to say that those nasty spikes are not present anymore in both configurations and the total ascent readings are now coherent with other tracking apps.

So the sensor seems to be just fine! It seemed to me also a problem related to the sensor holes placement... I'm wondering why not implementing an outlier filter to make the measure more robust...

Anyway, I can live with this, thanks!