When quadrature signals af- fected by offset and gain errors were simulated, we found that their influence is substantially greater than that of a phase shift error on the calculation of the ac- celeration spectrum. For example (see Fig. 10), when |q| = 0.1 was chosen, we observed a relative amplitude error in the order of some percent, whereas the phase errors were smaller than 0.004 rad within the range of k = 1,..., 6.