1.Article 1 is replaced by the following:‘Article 1The field covered by the survey referred to in Article 1 of Regulation (EEC) No 3924/91 is to be identified by reference to the survey population and the observation unit.The survey population of the reference period shall be enterprises whose principal activity or one of its secondary activities is listed in sections B or C of the classification of economic activities in the European Community (NACE Rev. 2), set out in Regulation (EC) No 1893/2006 of the European Parliament and of the Councilnote.The observation unit shall be the enterprise as defined in Council Regulation (EEC) No 696/93 on the statistical units for the observation and analysis of the production system in the Community. Member States may collect data using another statistical unit as observation unit as long as they transmit enterprise data to Eurostat.