The vehicle representative of its type shall be considered as complying with immunity requirements if, during the tests performed in accordance with Annex VI, and subjected to a field strength, expressed in volts/m, of 25 % above the reference level, there shall be no abnormal change in the speed of the driven wheels of the vehicle ... The field generating device type(s) shall be chosen such that the desired field strength is achieved at the reference point (see paragraph 5.4 of this Annex) at the appropriate frequencies.