SAP Note 20043 - Exchange rate in document header wrong?

Symptom

The exchange rate displayed in the document header does not correspond to the relationship foreign currency amount/local currency amount in a document item.

Cause and prerequisites

The exchange rate in the document header is not intended to represent the exchange rate of the document lines.
The exchange rate in the document header is only intended to show the exchange rate that was used for automatic translations when only one of the two amounts (foreign currency amount or local currency amount) was entered during document entry.
The task that many users intuitively assume is performed by this field - representing the relation foreign currency amount/local currency amount - cannot in fact be performed by this field.
The reason for this is that the exchange rate relation can differ from one document item to the next. This is the case, for example, when both amounts were manually entered and different exchange rate relations were used. Another typical example is the clearing of foreign currency documents in which the bank posting, clearing posting, and any residual items or partial payment items were performed at different exchange rates.
It therefore makes more sense to display the required information at document item level, and not in the document header.

Solution
The exchange rate of the item can be displayed in the line item display. This is back-calculated from the foreign currency amount and the local currency amount. Function module CALCULATE_EXCHANGE_RATE is used to do this .
To display this exchange rate, define a line layout that contains the field 'Effective exchange rate' (field name: RFPOS-KURSE).