Phoenix 7 measuring wrong distance while using running function

To get the best GPS position you should use All + Multi-Band. Auto select will try to use the best option but will still prioritize battery life.

In a city with lots of reflections and blind spots from buildings GPS will always have issues.

Fair. Though 2 thirds of Frankfurt marathon are in the suburbs / country side with low buildings or no buildings at all. I could notice that the inaccuracy was increasing throughout the race.

I can understand being off 200-300m. 2km seems way too much 

Could you post a link to the activity? Wrong distance is often not caused by GPS errors, but rather by inaccurate running stride length calibration. The watch uses the combination of GPS and accelerometer data to estimate the pace and the distance. Though, the watch has to be properly calibrated (sufficient number of runs under good GPS conditions) in order to calculate the pace & distance properly. With the access to the activity we could tell what was the primary reason of the distance error in your case.

Unfortunately, it is not possible to reset the wrong calibration easily with a standalone watch - you'd have to do the master reset to factory defaults. It is much easier if you use the HRM-Pro chest strap - not only the estimate with the accelerometer of the strap is typically an order of magnitude better, but you get the full control over the pace & distance calibration in the HRM-Pro sensor settings - you can reset and restart the calibration if you are not happy with it, and you can halt the continuos calibration once you are satisfied with the accuracy.

https://connect.garmin.com/modern/activity/17390173132

There you go. The report is also showing some inconsistences and mistakes. If you see the overview page it says the activity was 42.81km but on the laps report it shows >44km, which is what I saw during the race.

For background. I have been using an HRM-PRO plus.

Thank you for suggestions.

The GPS track seems to be OK. When saved as Course, it shows the distance of 42.81 km too. It would be significantly different than the activity distance if there were important GPS glitches.

It does not look like you edited the activity distance manually, since the activity details tell "Summary Data: Original". Or did you? And from the time data of the activity it is also apparent the auto-pause function was not used either (Time, Moving Time, and Elapsed Time are practically identical), so I do not know why the laps do not match the total distance. I do not remember seing such case yet. Some digging into the detailed raw data of the FIT file could perhaps offer some clues, but frankly told I do not feel like going to spend the time on it right now. I recommend contacting the Support, and emphasizing the discrepancy between the total distance of the laps vs the total distance of the activity - that's something what should make them clear immediately that there is something wrong with it.

BTW, what are the Pace & Distance settings at your HRM-Pro? Did you keep it in the default "Indoor only" mode? That's definitely the way it should stay. I strongly discourage from using the "Outdoor" option. In fact the feature is used outdoors, even with the "indoor" option too, but only as the fallback. In the "outdoor" setting it would be used exclusively, and it would void proper calibration, and would skew the results considerably.

BTW, the difference between the total and laps distances is 3.7%. Do you see the same discrepancy in shorter runs? If so, then I would reset the pace & distance calibration in HRM-Pro settings, and do it anew. Be sure to keep the "indoor only" option at both pace and distance measurnment.

trux said:

Did you keep it in the default "Indoor only" mode?

Just to add my 2 cents: 

It seems that Garmin changed the default setting to always use HRM Pro data for distance measurement. I helped a lot of people in the Fenix 6 and 7 forums with a very similar issue and the problem was mostly that this setting to use the HRM Pro to calculate the distance instead of GPS. 

#Matthias# said:

It seems that Garmin changed the default setting to always use HRM Pro data for distance measurement.

I did not see it yet. I recently connected HRM-Pro to two watches, and the default setting was still "Indoor". They were not Fenix watches, though. And TBH, I would be surprised if Garmin really changed it, because the calibration cannot work in such case, and it would be completely useless. They tell it themselves in the document Calibrating the Pace and Distance Feature on a HRM-Pro or HRM-Pro Plus | Garmin Customer Support. I would rather bet that the users changed the setting themselves, either intentionally, or inadvertently. 

thanks! If this is the case, how can I fix it?

It was set as indoor though the auto calibration was On, should I turn it off? What else could it be the problem?