I think there's a setting for whether it will try to self-calibrate (from GPS) when you turn it on or start a ride. Garmin's watches can self-calibrate (again from GPS) continuously over the course of a ride or a run or a hike, I don't know if their bike computers have that or not. Some of them will self-calibrate when you go by a saved location, I don't know what controls that. The idea is if you save "home" or whatever as a place and give it the correct elevation, that's a pretty reliable thing to use.

Instead of breaking a ride up into several recordings, there's a way to calibrate manually in the menu. Of course where that is, is different in every model... But you could do that every time you go by an elevation sign or whatever, if you wanted to.