A method of determining variations in operating characteristics of a
mechanical system having a rotatory mode of operation. There are provided
the steps of first monitoring operating impulses generated by the
mechanical system during a first interval of operation; first analyzing
the operating impulses obtained during the first interval to determine
the intensity and frequency of the operating impulses; first correlating
the operating impulses obtained during the first interval to
corresponding angular positions of the rotatory mode of operation; and
first producing a first record of the intensity and frequency of the
operating impulses obtained during the first interval correlated to the
corresponding angular positions of the mechanical system. These steps are
repeated to form trend data that results from comparing the first and
second records to determine differences in the operating impulses
obtained during the respective first and second intervals correlated to
the corresponding angular positions of the mechanical system.