21.2. If the non-delivery of any of the goods prevents the normal use of the supplies as a whole,  the liquidated damages provided for in Article 21.1 shall be calculated on the basis of the  total contract price.  21.3. If the contracting authority has become entitled to claim at least 15% of the total contract  price it may, after giving notice to the contractor:   seize the performance guarantee; and/or  terminate the contract,  enter into a contract with a third party for the provision of the balance of the supplies  at the contractor's cost. 22.1. Contract amendments must be formalised by a contract addendum signed by both parties  or by an administrative order issued by the project manager or the contracting authority.  Substantial amendments to the contract, including amendments to the total contract price,  must be made by means of an addendum. Any contractual amendments must respect the  general principles defined in the practical guide.  22.2. Subject to the limits of the procedure thresholds set in the practical guide, the contracting  authority reserves the right to vary by an administrative order the quantities per lot or per  item by +/- 100 % at the time of contracting and during the validity of the contract. The  total value of the supplies may not rise or fall as a result of the variation by more than  25% of the tender price. The unit prices quoted in the tender shall be applicable to the  quantities procured under the variation. 22.3. The project manager and the contracting authority shall have the power to order any  amendment to any part of the supplies necessary for the proper completion and/or  functioning of the supplies. Such amendments by administrative order may include  additions, omissions, substitutions, changes in quality, quantity, form, character, kind, as  well as in drawings, designs or specifications where the supplies are to be specifically  manufactured for the contracting authority, in method of shipment or packing, place of  delivery, and in the specified sequence, method or timing of implementation of the tasks.  No administrative order shall have the effect of invalidating the contract, but the financial  effect, if any, of all such amendments shall be valued in accordance with Article 22.7.  22.4. All administrative orders shall be issued in writing, it being understood that:  a) if, for any reason, the project manager or the contracting authority finds it necessary  to give an order orally, it shall as soon as possible thereafter confirm the order by an  administrative order;  b) if the contractor confirms in writing an oral order given for the purpose of Article  22.4.a and the confirmation is not contradicted in writing forthwith by the project  manager or the contracting authority, the project manager or the contracting  authority shall be deemed to have issued an administrative order;  c) no administrative order is required to increase or decrease the quantity of any  incidental siting or installation because the estimates in the budget breakdown were  too high or too low.  22.5. Save where Article 22.4 provides otherwise, prior to issuing an administrative order, the  project manager or the contracting authority shall notify the contractor of the nature and  form of such amendment. The contractor shall then, without delay, submit to the project  manager a written proposal containing:  August 2020 c4e_annexigc_en  Page 17 of 36  Article 22 -  Amendments 