To provide a method for determining frequency values associated with force applied to an instrument.

This method contains a step (64) of calculating a plurality of 1st spectrum amplitudes, associated with 1st forced waveform applied to the instrument; a step (84) for calculating a plurality of 2nd spectrum amplitudes, associated with 2nd forced waveform applied to the instrument; steps (78, 98) of calculating the maximum spectrum amplitude, based on these plural 1st and 2nd spectrum amplitudes; a step (102) of determining amplitude threshold based on the maximum spectrum amplitude and the acceptable values; a step (104) of determining a plurality of 1st target frequency values, by selecting the frequency values associated with the subset of the 1st plural spectral amplitudes equal to or greater than the amplitude threshold; and a step (106) for determining a plurality of 2nd target frequency values by selecting frequency values, associated with the subset of the 2nd plural spectrum amplitudes equal to or greater than the amplitude threshold.