If you already have one, make sure not to misspell it. (Check out the Leaderboard to confirm your username).
To add a new user or switch to a different user, enter "rr", save, and then reenter the username.
To change the username of the current user, just enter the new username without first entering "rr".
WARNING: Not following the correct procedures for when and when not to enter "rr" first will result in incorrectly storing the data.
