Abstract: Method and apparatus for engine and rotary machine analysis provides a vibration sensor adapted to produce a plurality of superimposed waveforms corresponding to engine or machine operating parameters including rotational speed. The signals are transmitted by an RF transmitter/receiver system in analogue modulated form to a data capture and analytical function unit utilising a software sub-system in which a power spectral density plot is produced containing a signature characteristic of the engine or other machine under test. This signature is recognised by a signature detect algorithm which can recognise and trace the signature across the frequency spectrum covered by the apparatus so as to provide a continuous tachometric function not requiring the filtering-out or other removal of irrelevant data. A diagnostic function arises from detection of the presence of additional harmonic peaks within the signature.