The Commission submitted on 21 June 1991 a proposal for a Council Directive on the approximation of the laws of the Member States relating to units of measurement (SEC(91) 1047). It concerns units of measurement used for economic, public health, public safety or administrative purposes; establishing a transitional period for phasing-out units not compatible with the International System of Units (SI) deriving from the Metre Convention (Paris, 20 May 1875) to which all Member States adhere. It is advisable for the Community to adopt the international solutions incorporated in ISO Standard 2955 of 15 May 1983; in addition the millimetre of mercury is to be retained with the kilopascal for measurement of body fluid pressures, and the barn is to be authorized for the description of effective cross- sectional area in nuclear reactions. An annex sets out legal units within the meaning of the proposed Directive. With exceptions in stated fields, Member States shall implement the Directive not later than 31 December 1999.