209Furthermore, the requirements of legal certainty and speed which apply in the context of control of concentrations mean that both undertakings and competition authorities can in principle rely on a foreseeable criterion and immediate access. In those circumstances, the turnover to be taken into account in order to determine the authority competent to examine a concentration must, as a rule, be calculated on the basis of the published annual accounts. It is therefore only by way of exception, where particular circumstances so justify, that certain adjustments should be made in order to best reflect the financial position of the undertakings concerned.