Quote Originally Posted by jobob View Post
When I start & end my ride at the same place, usually the total ascent/descent values (and the start/finish altitude) agree within a few percent, but once in a while they're very different. I assume that's because of weather changes over the course of my ride.
I get that a LOT if I start from home. I concluded that it's because it is hard to get a good satellite lock from my house in all the trees, and even though it "says" it has the satellites I think it really takes some time for them to lock on. (My car Garmin won't even try to figure out where we are til we've got all the way down to town.)

Your reason makes a lot of sense as well. I'm sure there are a lot of variables.