It does the computation automatically whenever you ride at/near threshold for a certain amount of time. When the ride gets finalized, it will pop up the VO2 max number on a little colored wheel. If you're not looking at the screen after you hit save, you'll probably miss it. I thought it would be stored in the Connect App under performance, but mine just says "No data" for both VO2 and FTP. Perhaps I don't have enough data recorded (only 10 rides since I got the 520) for it to update in the app? Dunno. Time will tell.