I have a few Garmin devices and use them when I run or cycle. Over the course of using them, I did notice some differences in them. Some I realize while riding, while some I notice when I start making videos on Virb Edit.
Only now that I managed to compare 4 device recording the same ride, connected to the same sensors, generated a video for each device using Virb Edit, and merged the 4 videos using another app to show the differences using the profile graphs.
?????Its a good way to confirm (or if you need evidence) to support things you see while riding, like drops in readings, weird gradients, etc.
https://youtu.be/VnLPqdOv0PM