Fig. 6. The frequency response characteristics of our force measurement system, M(j). This style of figure is called a `Bode plot', and shows the magnitude and phase differences plotted against logarithmic angular frequency. The frequencies used for the measurements (0.9, 1.8, 3.6 and 7.4 Hz) are equal to 5.6, 11, 22 and 46 rad s^-1, respectively. (A) The gain in decibels; (B) the phase differences. Note that the gain is attenuated and the phase lag enlarges with increasing frequency, which should be compensated for in the analysis.