Sure, you can have as many devices as you want under one login. When installing on an additional machine / reinstalling on the same machine just check the box that says 'Previous Member' (if I remember that correctly) and sign in with your login and password. By default Devices show up under your login for 1 week after installation and 2 weeks after a result is returned. You can change this behavior using drop down menus. Each installation produces a unique Device, though all points / results are totalled under the Member ID (login). Devices cannot be combined. Login names can be changed, as can passwords.