27.34. Correlation tables provided by the World Customs Organization (WCO). WCO produced the first version of the HS in 1988 (HS88). In 1986, it had issued a publication entitled “Correlation Tables between the Harmonized System and the 1978 version of the CCCN”, to link HS with the Customs Cooperation Council Nomenclature (CCCN). This was a two-way correlation, that is, from HS to CCCN, and from CCCN to HS. When HS is revised, the WCO issues correlation tables between the new and preceding versions of HS and makes them publicly available.
27.35. Correlation and conversion tables available from UNSD. UNSD has created correlation and conversion tables between various versions of the HS, SITC and BEC, so that it could maintain its time-series data on trade. UNSD also maintains correlations and conversions between HS, CPC and ISIC. If compilers need to convert their data from one classification to another, it is good practice for them to take into considerations correlation and conversion tables available from international and/or regional organizations.
27.36. Correspondence tables with non-HS national commodity classifications. If a country compiles data in terms of a non-HS classification (provided that said classification is highly detailed, with criteria similar to the ones applied in HS), compilers are advised to develop a correspondence table between the non-HS classification and HS, and to make it available to interested users.
 This text was initially known as the Brussels (Tariff) Nomenclature (BTN), but in 1976 it was renamed the Customs Co-operation Council Nomenclature (CCCN), to prevent any confusion regarding the international organization responsible.
 See http://www.wcoomd.org/en/topics/nomenclature/instrument-and-tools.aspx.
 UNSD converts data based on the most detailed level of the applicable classifications.
 See http://unstats.un.org/unsd/cr/registry/regot.asp.