The unconditional promise to pay a certain sum of money and their interests The note, unlike the bill of exchange, has an unconditional promise to pay a sum of money and their interests in domestic or international equivalent. The sum must be expressed in number (s) and letters, as the currency in which the payment. If paid in foreign currency must indicate the exchange rate between the currencies or equivalent, to be taken into account when due. This requirement is what distinguishes it from other bonds.