(18)The GPA applies to contracts above certain thresholds, set in the GPA and expressed as special drawing rights. The thresholds laid down by this Directive should be aligned to ensure that they correspond to the euro equivalents of the thresholds of the GPA. Provision should also be made for periodic reviews of the thresholds expressed in euros so as to adjust them, by means of a purely mathematical operation, to possible variations in the value of the euro in relation to those special drawing rights. Apart from those periodic mathematical adjustments, an increase in the thresholds set in the GPA should be explored during the next round of negotiations thereof.