“…As one result of a workshop held at PTB in 2006 [2], an iMERAPlus joint research project is now coordinating the European activities to determine the Boltzmann constant in Spain (Centro Español de Metrología, CEM), Denmark (Danish Fundamental Metrology, DFM), France (Institut National de Métrologie, LNE-INM/CNAM, and University Paris North), Italy (Istituto Nazionale di Ricerca Metrologica, INRiM, and Universities of Naples and Milan), United Kingdom (National Physical Laboratory, NPL), Germany (Physikalisch-Technische Bundesanstalt, PTB) and in the European Institute for Reference Materials and Measurements, IRMM [3]. In this major European research project, the partners use different methods to determine the Boltzmann constant aiming at a relative standard uncertainty on the level of a few ppm.…”