What is the formula for calculating Exchange Variance adjustment?

Summary:

A journal entry has been generated for a PO for the Event Type and Event Class 'Invoice Price Adjustment'. The event a journal entry line for Receiving Inspection and Exchange Variance adjustment. What is the formula to output the value of Exchange Variance Adjustment?

Content (required):

An FCY (foreign currency) PO has been created, received and invoiced. The PO line has been created with an Expense stock-able item and the Destination Type of the PO line is Inventory.

The receipt and Invoice exchange rates are the same as both were created on the same day, while the PO exchange rate is different. Upon running Create Accounting for Receipt Accounting subledger, the Event 'Invoice Price Adjustment' was created.