Basic Custom Scrollbar Problem

Hi Folks,
I also have what will turn out to be a very basic oversight with the custom scrollbar.

I too have followed the tutorial to the letter but have a very annoying problem.

The scrollbar and scrollface work fine (with a minor modification to the script - stoppintg the scrollface/drag object going too high).

However when using the up and down buttons :
1 the up scrolls the content area to far
and
2 the down butoon does not move the content area far enough

Can anyone please help

Cheers

J