(7)For the purposes of calculating turnover, both in the Union and in trading venues outside the Union, to determine the principal trading venue of a share, each relevant competent authority needs to determine the relevant sources of information to identify and measure the trading on a specific share. There are currently neither harmonised transaction reporting requirements in the Union for shares admitted only on multilateral trading facilities nor international standards with regard to trading statistics on individual shares on trading venues, which may show relevant variations. Thus, it is necessary to allow some flexibility to competent authorities to carry out that calculation.