Originally Posted by
rdtompki
I think we would need to know the nature of the filter used to calculate altitude. If the OP's previous ride started/stopped at a higher altitude it might take some time (
TBD) for the GPS component of the to get a good altitude fix. which could account for the slope on what is essentially a closed circuit.
That altitude in that track is not from GPS. The Edge 500 he was using (I use one too) has a barometric altimeter similar to what is used on aircraft. It pretty accurately reads the altitude change per lap based on small changes in air pressure with altitude. The total ride took about an hour. As the barometric pressure rose, the reported altitude went down. Barometric pressure changes like the one on that ride are fairly common, but not an every day occurrence, and usually indicate a significant change in the weather.