How Elevation is calculated
It is important to remember that elevation data from all sources (barometric altimeters, GPS signals, and databases) is subject to error and that the elevation gain for a workout is an estimate. We are always working on improving our elevation data sets and algorithms.
If your workout was recorded with the mobile app or with a GPS device that does not have a barometric altimeter, XOSS will use your workout GPS data to "look up" the elevation for each point you record. We do some smoothing to the data, which includes discarding outliers to reduce noise. The amount of smoothing is more for workouts without barometric data than it is for workouts with barometric data. While we attempt to match the path of your workout with the actual trails and roads in the area, elevation calculation is still somewhat dependent on your GPS data and the accuracy of the database for that region.
Barometric altimeters
Barometric altimeters determine altitude by measuring atmospheric pressure. Measurements can be affected by changes in the weather or the sensor holes getting blocked by water or other debris.