Understanding the movement of the main resonating surface
of an instrument, in the case of a guitar, its
top-plate, is essential in understanding the instrument's ability
to propagate sound at all frequencies. Viewing the frequencies at which the modes
occur helps explain the timbre of the acoustical characteristics
of the instrument. A scanning-point vibrometer, for example by Polytec, measures
the movement of a surface and gives
its users three-dimensional software views of its structural motion.