After uploading it via Connect Mobile (On Android), I was surprised by the pace.
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As you can see here, there are about 400 meters more from... somewhere?!?
Due to the fact, it was a regeneration run, I´vent touch the 5:12 at any time:
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The activity can be found here. -> Not anymore. Fixed distance now, manually.
The protocol on my Vivoactive says:
Distance: 8.04km
Pace: 5:26/km
Of course, I did not modify the activity by hand or something. Just upload, rename and classify it.