Trackingn The Material

Dear Experts,

Is there any report or process in SAP to know the changes happened toa material Ex: I purchased a material on 01.01.2011.

Because of Moving Average Price the price of the material got updated cause of the PO created in every month/ Now the price of the material has been chanegd and I would like to know the details of the documents that cause the change for the material.

Please help. thakns