170With regard to the principle of legal certainty, the Court has consistently held that this principle guarantees that rules are ‘clear and precise, so that individuals may be able to ascertain unequivocally what their rights and obligations are and may take steps accordingly’ (Case 169/80Gondrand Frères and Garancini [1981] ECR 1931; Case C-143/93van Es Douane Agenten [1996] ECR I-431, paragraph 27; and Case C-110/03Belgium v Commission [2005] ECR I-2801). This does not mean that calculation of the turnover should be ’easy‘ in every case and does not justify failure to take into consideration all the available information. Endesa notes that reconciliation of accounts is an obligation under Community rules which a prudent trader is deemed to have been aware of for several years and that the protection of traders is not justified ‘if a prudent and circumspect trader could have foreseen that the adoption of a Community measure is likely’ (Joined Cases C-37/02 and C-38/02Di Lenardo and Dilexport [2004] ECR I-6911, paragraph 70). In this case, the IAS/IFRS were clear and unambiguous, and prudent and circumspect traders were aware of them at the time the bid was made, so there was no infringement of the principle of legal certainty.