My wife and I both use the 910. We went on the same bike ride but after uploading to Garmin Connect we came up with different reports for: Elevation Gain/loss, by 500 feet? Anyone have any idea why, or if we need to do some software updates? Thanks Hg
The elevation is determined using a barometric altimeter on the 910. You could see differences in the elevation change because of a poor GPS fix when starting your activity, calibration error, air temperature and pressure differences, or a host of other reasons. The workaround is to use the Elevation Corrections option on your activities after they've been uploaded. Unfortunately that functionality is disabled for a while.
The 910 allows you to specify map points with elevation data. It will use the elevation data you provide to calibrate the barometric altimeter. This is covered in the section entitled Calibrating the Barometric Altimeter in the 910XT manual. If you want your devices to display more consistent results, you might want to add a few of these points to each device so that it will calibrate when you go out for your workouts. Another thing that may help is to be sure that the device gets a good fix before starting the activity. Letting it sit for a few minutes after satellites have been acquired wouldn't hurt.
