Method for determining the slip of a machine which comprises the steps of: receiving a measurement signal, wherein the measurement signal includes a set of measurement values of an operational parameter of the machine; determining the frequency spectrum of the measurement signal by converting the measurement signal into the frequency domain; determining whether the frequency spectrum includes at least two peaks in the frequency spectrum for which different types of failure mode calculations return the same slip value; wherein, if in the determining step it is found that two peaks exist in the frequency spectrum which return the same slip value, said value is determined to be the slip value of the machine.