Using the game "Battleship" to demonstrate Agile

I found this idea posted on a blog (http://adaptagility.co.uk/agile-games-battleships) and have used it in my class when we start to talk about Agile methods. You can read the details in the referenced link above, but the way I use it is as follows:

Note: If you don't have a Battleship game of your own, you can get them cheap on ebay.