I'm onto my second Edge 530 and the same fault has developed with altitude readings - am I doing something wrong? After several months of flawless operation, in the middle of a ride I started to get really odd altitude readings and corresponding gradients (for example altitude would suddenly go from 100m to 10m and then not change even when climbing 200m, the corresponding gradients would show as negative when climbing and vice versa for descending). When I got home from the ride and downloaded to Garmin Connect, the ride altitude profile would look nothing like the ride just completed. The first time this happened I rebooted the 530 and went back to factory settings but this didn't fix the problem. I took it back to the store I bought it from and they tried a few things with no success and finally they sent it to Garmin. After a week Garmin instructed the store to give me a new 530. I've had this two months and, lo and behold, same problem has appeared after over 2000 kms of successful operation. Have tried re-booting and going back to factory settings but problem persists - any ideas?