Please feel free to use the subscribe button even if you already have issue 1. If you use the same email address then you'll automatically be subscribed for an extra 12 issues, not charged twice for the first issue. If you use a different email address just send me a quick note to let me know (gareth@sudokuxtra.com) and I'll make sure things work out correctly!
By the time issue 2 is out I hope to have the option to create a Sudoku Xtra 'account' listing all the magazines you've bought and which are still available to buy.
Gareth