The official publication of the International Temperature Scale of 1990 (ITS-90) gives a concise definition of temperatures T90 and is highly prescriptive. To accompany the text, supplementary information concerning the practical realization of the scale was published in 1990 by the BIPM in a monograph entitled Supplementary Information for the ITS-90; this monograph provided the non-prescriptive details in a comprehensive form.
A first revision of the initial edition was completed in 2018 and takes into account the progress in thermometry that have been achieved since 1990 concerning both temperature fixed points and interpolation instruments. The new edition has been drafted by the CCT Task Group for the Realization of the Kelvin (CCT-TG-K) and each chapter has been approved by the Consultative Committee for Thermometry.
This new edition, Guide to the Realization of the ITS-90, is published uniquely in electronic form on the BIPM website. The chapters are self-contained but harmonized allowing a higher flexibility for future revisions to follow the pace of new developments. The presented material could be assembled only thanks to the continual assistance of many colleagues in the temperature-measurement community.
There are many sources of information which requires a subjective selection of the references and unintentional errors of omission are certainly inevitable; comments and proposals for future revisions are most welcome.