Need help with this array/position problem

programming flash
1

I have a scroll pane component with SWFs loaded in them vertically like a PDF viewer. I need to be able to change the page indicator when the user scrolls.

I have an event listener on the scroll pane listening for scroll.

I have an array of the Y values of each page; looks something like this:
0,800,1600,2400,3200 etc

What kind of equation would I do to determine the correct number.

My scroll event looks like this:


private function checkYValue(e:ScrollEvent):void
{
    var currentY:Number = (e.position + PAGE_SPACING) / PAGE_SPACING;
   /* traces out these kind of values
   1.05
   1.055
   1.06
   1.065
   1.07
   */		
}

currentY is obviously the Y position of the scroller in pixels starting from 0.

So with that said, how could I change the page number based off of currentY?