The text of the International Temperature Scale of 1990, ITS 90, gives a concise definition of temperatures T90. It is highly prescriptive and formal, and does not contain supplementary information concerning the practical realisation of the scale. Such non-prescriptive information is provided in the Supplementary Information for the ITS-90 in a form as extensive and comprehensive as possible. The first edition was published as a monograph by the BIPM in 1990. The present edition takes account of a large number of advances in thermometry, concerning both temperature fixed points and interpolation instruments, that have been achieved in the intervening more than twenty years. It has been prepared by Working Group 1 of the CCT and approved by the CCT.
Starting with the present edition, the Supplementary Information will be published only electronically on the BIPM website. The chapters and some sections are self-contained, but harmonised documents with the responsible members of Working Group 1 as authors. This enables more flexibility for necessary future revisions considering new developments. The documents are accessible via links in the contents listed below. For those parts, for which an actual revision is not yet available (no link), the 1997 reprinting of the 1990 edition presents still useful information.
The material contained in the documents could be assembled only thanks to the continual assistance of many colleagues in the temperature-measurement community. The members of Working Group 1 highly appreciate this assistance. There are many sources of information, which requires a subjective selection of the references by the responsible members. Unintentional errors of omission are certainly inevitable. Comments and proposals for future revisions delivered via the CCT are, therefore, warmly welcomed.