how to report on the Value of a PO Tax out after complete

When a PO is complete and sent to AP the value of EXTEND is set to 0.00   i can reference SCAMOUNT which seems to hold the original value after completion of the PO but it is tax in.  I need to know the original value for reporting tAX out.  I can't find any way field that maintains the value that was originaly in EXTEND or any way to calc it as all the tax fields that i can see are all set to 0.00 also.  Is there another table or some other way i can calc it?