Five examples are given of investigations of specific problems on real plant using a combination of the techniques described in earlier chapters. The case was a study of developing rotor crack in a large turbo-alternator over a period of about two months. The analysis was at time confusing and extensive analysis was employed to reach a conclusion. However, it proved successful in avoiding possible catastrophic damage. The next case arose from the first as the rotor was removed from the machine and tested in a workshop. Whereas the crack was diagnosed using forced response, location of the crack requires examination of the natural frequencies and mode shapes. This is straightforward for an axisymmetric rotor but not for an alternator as discussed. The third study presented concerned the regular failure of a set of pumps which involved installation of instrumentation to monitor torque variations. However, results were complex and required the development of same models. The combination of measurements and model led to a satisfactory solution. The vibration problems on large fans with overhung rotor demonstrate the crucial importance of gyroscopic term on such machines. The designers had ignored them. Finally, an on-going problem of turbine low pressure instabilities is briefly summarized.