Just upgraded to a 945 and haven't gotten rid of my 935 yet.
When I look in Garmin Connect the Training Status for each watch is different, even though when I set up my 945 I said to bring over all of my training history (& FirstBeat stats) so that the 945 would already know my VO2 max etc.
Do different devices use different algorithms for calculating performance metrics (Training Status, FTP, VO2 max, etc...)?