Complete Offtrack ~4km

There are multiple reasons for this to happen, but in short it means the watch lost connection with one or more satellites, because of trees, clouds, tall buildings, microwave interference or whatnot. An example of the last one would be: on my way to work, I walk along a military building and an antenna and around them the signal is always scrambled. I always "jump" around 20 meters to the side there.

The other possible explanation is it picked up a reflected signal which lead to miscalculations. This should not happen so often, since all GPS trackers try to correct such errors, but unfortunately, they fail sometimes.

And finally, if this happens often, you may have a faulty unit.

Thanks, I'm gonna keep looking at it.

Additional i get this.....and i dont now why. Complete flat. 654m Height difference are not possible. And that on both of my to rounds.

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I can't comment just by seeing that. If you could provide the elevation chart, then it may make more sense.

All I can say is, if it happens all the time and at the same place, something is disrupting the signal there.

trux said:

At Instinct the elevation data comes from the barometric altimeter, so the GPS signal has no influence on it.

Yes and no. GPS (or DEM) is used to determine elevation every time the altimeter is calibrated. After that the altimeter measures pressure changes to determine altitude changes. In other words, the barometer is used only between each two calibrations.

So, when starting (or resuming) an activity, while the location is not fine calculated, there could be several points with random positions and random altitude that would affect the summary.

However, now that you mentioned 650m ascent over 20km may not be that much. Indeed, this could easily accumulate over small bumps.

sspanak said:

GPS (or DEM) is used to determine elevation every time the altimeter is calibrated.

Yes, but only if the option "auto-calibration during activity" is enabled. Not sure whether it changed recently, but by default that option used to be disabled.

Besides that, I am not at all sure how often the auto-calibration happens (if at all) during the activity even with the option enabled. From the values seen on the elevation profiles of many activities (not only on my own ones), I have some doubts it happens too freqently, or at all. For example even with the option on, very frequently the elevation at the very same point will differ each time you pass through it (despite that the GPS position is detected fine). The most typical case is when you come back to the starting point and the elevation profile shows the altitude tens of meters different than when you started. Happens practically anytime. For this reason I am almost always turning on the Elevation Correction on my activities.

Honestly, I don't remember what is the default setting, but I keep auto-calibration on and it has been accurate enough for me.

And you are absolutely right. I've noticed the elevation differences when I go back to the starting point, but if I cared about accuracy under 10-15 meters, I wouldn't be using a GPS watch, would I?

However, if we go back to the original topic, Hexxer is complaining about an error in the matter of hundreds of meters. This either means he/she doesn't realize the small bumps accumulate into big ascent, or something is very wrong with the measurements. This is why I asked for the elevation chart - to see if there is something suspicious.

sspanak said:

or something is very wrong with the measurements.

... or, as I wrote, the watch's altimeter simply adds elevation gain due to wind gusts, and due to the modified air flow caused by the variabilities in speed, as it is quite usual with Instinct, unless you protect the pressure sensor hole. Not speaking about sweat cummulating under the hole, which is also an issue that can easily add wrong pressure readings.