Vibration measurements may be required for a variety of reasons of which the following are the most important: a) design/development evaluations; b) in situ testing; c) as information for a condition-monitoring or machinery health programme (ISO 14694 and Annex C gives recommended measuring positions for machinery health measurement); d) to inform the designer of associated supporting structures, foundations, ducting systems, etc., of the residual vibration which will be transmitted by the fan into the associated structure; e) as a quality assessment at the final inspection stage; f) to be sure of acceptability of specific dynamic loading.