Units have always been something of a necessary evil to scientists and engineers. International use of standardized units has been a desirable goal for many years. With the United Kingdom, and other countries, now well on the way to adoption of the metric system, there is every prospect of considerable reduction in future of the present confusion caused by the use of different sets of units. As a contribution to this progress of rationalization, the Journal of Sound and Vibration is adopting the internationally recommended system of metric units, the Systeme International dUnit& (SD. Authors are asked to use these units in their work. Information about the system can be obtained, for example, from the British Standards Institution publication PD 5686, ‘The use of SI Units”. P. E. DOAK