Is there a report available on change orders ?

Hello,

We are looking for a report which gives all the details of Purchase orders changed  in a period of time.

This is for audit purposes to know how people are changing orders.

I am talking about Change orders here.

ie.

1) Requestor created a requisition

2) approver approved it

3) Approved Purchase order is automatically generated

4) Now requestor goes and changes the requisition

5) approver approves again

7) Change order is created with a revision. ---- We wish to track the changes made like this.

Is there an inbuilt report available.

If not what will be the logic to write one.

Many Thanks,

Mikaela