illustrate individual acoustic signals having larger time intervals separating them from other signals as the coating 26 of a vane deteriorates the magnitude of the peaks 50 will increase in the same manner illustrated in fig6 8 and described above the sinusoidal displays 48 a 48 b also include larger peaks 52 a 52 b created by the pressure pulse created by a blade 18 passing a vane 22 fig9 illustrates a sinusoidal display 48 a wherein all blades 18 and vanes 22 have intact coatings 26 and therefore all peaks 52 a are the same height fig1 illustrates a sinusoidal display 48 b wherein all vanes 22 have intact coatings 26 but one blade 18 has a deteriorating coating 26 resulting in the peaks 52 b having a larger magnitude than the peaks 52 a such a situation should result in a sinusoidal display 48 b for all vanes 22 associated with the blade 18 having the deteriorating coating 26 because that blade 18 will generate the same pressure pulse while passing all such vanes 22 fig1 illustrates a sinusoidal display 48 c wherein the vane 22 to which the acoustic waveguides 28 30 in question are attached has a deteriorating coating 26 but all blades 18 have an intact coating 26 resulting.