(c) The frequency at which the percent error would be zero. (b) The percent error when the frequency of surface vibration is 600 Hz. (a) The equation of motion amplitude dm of the vibration of the surface determines the following: y = S*sin(t), a displacement y. If the amplitude zm of the motion of the mass relative to the box is used to measure the system with a known natural frequency of 120 Hz. The box is rigidly attached to a surface that moves with a vibrometer (a device used to measure the amplitude of vibrations) consists of a box with a mass-spring.