 The CGPM recognizes two classes of membership – full membership for those states that wish to participate in the activities of the BIPM and associate membership for those countries or economies that only wish to participate in the MRA programme.Associate members have observer status at the CGPM.Since all formal liaison between the convention organizations and national governments is handled by the member state's ambassador to France, it is implicit that member states must have diplomatic relations with France, though during both world wars, nations that were at war with France retained their membership of the CGPM.