The contractor is liable for any conformity defect which exists at the time of delivery, even if this defect does  not appear until a later date.  The contractor is also liable for any conformity defect which occurs after delivery and is ascribable to non- compliance with its obligations, including failure to provide a guarantee that, for a certain period, supplies  used for the purposes for which they are normally used or for a specific purpose will preserve their qualities  or characteristics as specified.  If part of an item is replaced, the replacement part must be guaranteed under the same terms and conditions  for a further period of the same duration as that specified above.  If a defect is found to originate in a systematic flaw in design, the contractor must replace or modify all  identical parts incorporated in the other supplies that are part of the order, even though they may not have  been the cause of any incident. In this case, the guarantee period must be extended as stated above.  II.4.2. Provision of services  II.4.2.1 Signature of the FWC does not guarantee any actual purchase. The contracting authorityis bound  only by specific contracts implementing the FWC.  II.4.2.2 The contractor must provide services of high quality standards, in accordance with the state of the art  in the industry and the provisions of this FWC, in particular the tender specifications and the terms of  its tender.  II.4.2.3 The contractor must comply with the minimum requirements provided for in the tender specifications.  This includes compliance with applicable obligations under environmental, social and labour law  established by Union law, national law and collective agreements or by the international  environmental, social and labour law provisions listed in Annex X to Directive 2014/24/EU, $^{4}$ as well as  compliance with data protection obligations resulting from Regulation (EU) 2016/679 and Regulation  (EU) 2018/1725.  II.4.2.4 The contractor must obtain any permit or licence required in the State where the services are to be  provided.  II.4.2.5 All periods specified in the FWC are calculated in calendar days, unless otherwise specified. II.4.2.6 The contractor must not present itself as a representative of the contracting authority and must inform  third parties that it is not part of the European public service.  II.4.2.7 The contractor is responsible for the personnel who carry out the services and exercises its authority  over its personnel without interference by the contracting authority. The contractor must inform its  personnel that:  (c) they may not accept any direct instructions from the contracting authority; and that  (d) their participation in providing the services does not result in any employment or contractual  relationship with the contracting authority.  II.4.2.8 The contractor must ensure that the personnel implementing the FWC and any future replacement  personnel possess the professional qualifications and experience required to provide the services, as  the case may be on the basis of the selection criteria set out in the tender specifications.  II.4.2.9 At the contracting authority’s reasoned request, the contractor must replace any member of  personnel who:  (c) does not have the expertise required to provide the services; or  (d) has caused disruption at the premises of the contracting authority.  The contractor bears the cost of replacing its personnel and is responsible for any delay in providing  the services resulting from the replacement of personnel.  4 OJ L 94 of 28.03.2014, p. 65.  17 