Anyone who says Garmin's elevation calculations are borked, you are correct. Contrary to what Garmin tells me this ride was neither underground nor underwater. : r/Garmin
Garmin Tread Off-Road GPS System Review | ATV.com
Garmin Tread Off-Road GPS System Review | ATV.com
Garmin Alpha 200i Handheld 9 Mile GPS Tracking & Training System | K9 Electronics
GPS: How pieces of metal in space know where you are | TerraHunt