This reference work provides comprehensive coverage of all the important units used in science, technology and medicine. Revised and updated, it also features descriptions of the international organizations responsible for the promulgation of both the definitions and the accepted values of basic physical quantities. The text includes the most recently accepted values of all units. Several disciplines which have in the past employed few scientific units are now introducing new units based on scientific principles and the dictionary has been extended to include examples of these. The dictionary aims to serve as a valuable source of reference to scientists in all disciplines who need precise definitions, as well as to the general reader who comes across units for the first time.