1. A process for obtaining the periodic component in a data vector of data taken of a sensed property of an element driven by one or more rotary components over several rotations comprising the steps of: forming said data vector asynchronously with respect to rotation of said one or more rotary components; receiving marker signals representing the rotation of the one or more rotary components; determining the periodic component of data in said data vector as a function of the data in said data vector and said marker signals; and determining the non-periodic component of data in said data vector by removing said periodic component of data from said data vector.