Contract number: ECHA/2020/666  II.20. PRICE REVISION  If a price revision index is provided in Article I.5.2, this Article applies to it. Prices are fixed and not subject to revision during the first year of the FWC.  At the beginning of the second and every following year of the FWC, each price may be  revised upwards or downwards at the request of one of the parties.  A party may request a price revision in writing no later than three months before the  anniversary date of entry into force of the FWC. The other party must acknowledge the  request within 14 days of receipt. At the anniversary date, the contracting authority must communicate the final index for  the month in which the request was received, or failing that, the last provisional index  available for that month. The contractor establishes the new price on this basis and  communicates it as soon as possible to the contracting authority for verification. The contracting authority purchases on the basis of the prices in force at the date on which  the specific contract enters into force. The price revision is calculated using the following formula:  Ir  Pr = Po x ( — )  Io  where:  Pr = revised price;  Po = price in the tender;  Io = index for the month in which the FWC enters into force;  Ir = index for the month in which the request to revise prices is received.  Payments are deemed to be effected on the date when they are debited to the contracting  authority’s account.  Payments are made in euros or in the currency provided for in Article I.7. The contracting authority makes any conversion between the euro and another currency  at the daily euro exchange rate published in the Official Journal of the European Union, or  failing that, at the monthly accounting exchange rate, as established by the European  Commission and published on the website indicated below, applicable on the day when it  issues the payment order. 39  II.21.3. Conversion  II.21.2. Currency  II.21.1. Date of payment  II.21. PAYMENTS AND GUARANTEES 