Hello SantJordi,
Thanks for getting back to us with those additional details. It looks like the same distance is measured differently on the Health app. Accuracy is very important, and we'd be happy to look into this with you.
"The Health app takes similar data from different sources, like steps recorded from your iPhone and activity from your Apple Watch, and organizes it based on where it comes from. By default, Health prioritizes data in this order:
Health data that you enter manually.
Data from your iPhone, iPod touch, and Apple Watch.
Data from apps and Bluetooth devices.
When you add a new data source, it appears above all other apps and devices that contribute data in Health. You can change the order of sources at any time. "
Manage Health data on your iPhone, iPod touch, or Apple Watch
If you're using an Apple Watch, let's try the steps in the following link:
Calibrating your Apple Watch for improved Workout and Activity accuracy
Message us back with your result. Kind regards.