System Transactions  If the conversion rate isn't defined for a specific transaction date, the application searches going back, up to 1 year to find the closest conversion rate.  For converting the transaction amount to the bank account amount the applications uses the Bank Conversion Rate Type (BANK_EXCHANGE_RATE_TYPE) from the bank account that corresponds to the transaction used.  For converting the transaction amount to the ledger amount, the application uses the conversion rate defined for the transaction.  For converting the transaction amount to the reporting amount, the application uses the default conversion type defined in the Currency Rates Manager.
If the conversion rate isn't defined for a specific transaction date, the application searches going back up to 1 year to find the closest conversion rate. Various conversion rate types are used for different conversions like from transaction amount to bank account amount, ledger amount, or reporting amount.
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How are conversion rates managed for System Transactions in Oracle Cash Management?