IP: FOX Month Function

Hi experts,

I need to revaluate the amount for a particular period where the user will assign a start and an end date. In back ground the revaluation should happen on the previous month and store on the current month. For example, if the data is like this:

Month: Amount

Mar 08: 100

Apr 08: 105

May 08: 110

Jun 08: 120

Jul 08: 130

Aug 08: 135

and the user wants to change amount for Apr 08 to Jul 08 by 10%, then in background i should calculate 10% increase on Mar 08 to Jun 08.

I am trying to write a fox. Can you please help how to read the first month and last month from a Period Interval variable. and how to use offset in FOX..

Thanks, Rishi