FOREWORD The formal decisions or agreements of the IEC on technical matters@ prepared by Technical Committees on which all the National Committees having a special interest therein are represented@ express@ as nearly as possible@ an international consensus of opinion on the subjects dealt with. They have the form of recommendations for international use and they are accepted by the National Committees in that sense. In order to promote international unification@ the IEC expresses the wish that all National Committees should adopt the text of the IEC recommendation for their national rules in so far as national conditions will permit. Any divergence between the IEC recommendation and the corresponding national rules should@ as far as possible@ be clearly indicated in the latter.