Having problems comparing 2 data tables.

[Jason_White]

My Data looks like this:

[TABLE="width: 500"]
<tbody>[TR]
[TD]Row Labels[/TD]
[TD]Total # of Students(m1)[/TD]
[TD]# of Jan 08 Students(m2)[/TD]
[/TR]
[TR]
[TD]2008[/TD]
[TD]9118[/TD]
[TD]758[/TD]
[/TR]
[TR]
[TD]Jan[/TD]
[TD]758[/TD]
[TD]758[/TD]
[/TR]
[TR]
[TD]Feb[/TD]
[TD]753[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Mar[/TD]
[TD]757[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Apr[/TD]
[TD]764[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]May[/TD]
[TD]778[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Jun[/TD]
[TD]777[/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

I'm running into a problem trying to compare 2 measures or tables. What I have is a measure with a count of ID#'s for a specific month and I want to see how many of those are still there or active in the subsequent months following.

How do i get powerpivot to look for the id#'s from the (758 Jan 08) in the (753 Feb 08) and return just the value that are still there?