I know a version of this question has been asked 20x so I'll say I don't care why they differ.
I just want to know: which version of elevation gain is more likely to be accurate? I often do rides in the Rockies where Connect says it's, say, 5k ft of gain, and when I'm done the watch says 3.8k ft despite following it exactly. Generally any ride w/ elevation gain will differ between the two sources by at least 500 ft if not a couple thousand...
I would think Connect is using topo or geological survey maps to baseline and is therefore more accurate than a janky baro sensor, but the confidence here doesn't seem to run high in Connect. Any thoughts?