Here, all the currencies that are going to be used by the currency payment type are set up.
To open Currency select General setup > Payments > Currencies
In the upper part of the window is a list of the valid currencies and the lower part includes an exchange rate for the selected currency.
The exchange rate per currency is set up with a start date and is valid until its next start date. It is very different between setups and, or countries how often the exchange rate is entered, every day, week or month.
You can keep track of the history of the currency rate by inserting each new exchange rate.
Please be aware that it is bad practice to edit the currency instead of creating a new line each time the currency rate changes.
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