When using project module to manage customer activity you might need to use fixed price project and invoice your customer by using milestone. In case of business with foreign currency, an exchange rate will be applied on your transaction. Sometimes the rate is fixed by an agreement (e.g for a specific milestone your client might fixed the exchange rate with his own customer at a specific date and post the invoice a couple of day later). In order to do this, we need to have the possibility to fixe the exchange rate at the milestone level (on account transaction screen) and not only in the project contract level which is currently the better way to achieve it. This idea aim to lead Microsoft to enhance the on_account (milestone) project screen in order to be able to lock the exchange rate use for a specific milestone.