My garmin was working fine up to a few days ago. On the front screen it shows speed and miles travelled, but now the miles travelled doesn't show. it shows all data when it goes on lap top. I have cleared storage but still nothing
Sounds like the distance field was removed from the display. I don't have a 810 so I don't know exactly how you add it back. However you can find plenty that do in the edge 810 forum. This is the forum for the Garmin Connect Website. Though I admit the "troubleshooting" category here is confusing.
