Sometimes you may notice a discrepancy between a calculation made on a mobile app (Garmin, Xert for iOS, Xert for Android) and the Xert Online web app.  This is often attributable to a difference in the fitness signature used in the calculation, where the server will update the signature after the activity is analyzed and may use a new fitness signature.  This can happen more frequently with the Garmin apps as their fitness signature used in the calculation can get stale if not updated during their initialization.  Sometimes errors can creep into the power data too that gets fixed by the server and not by the apps. Finally, sometimes it's from minor mathematical differences between the platforms that can occur.  In general, if the signatures that are used are close and the errors are not major, the differences should not be material.