Scroll edittext a 'page' at a time.

Hi,

I'm developing a text viewer app where I load a text file into an edittext box in fullscreen mode and all is working fine. I'd like to be able to scroll a 'page' of text at a time if the user clicks on the edittext box.
This is where I'm stuck, how can I calculate where selectionstart should be to 'scroll' down to the next page? Anyone have any ideas?

Regards

Boredsilly