As in the case of a spectrum from a prism, we can plot the amplitudes of all the frequency components versus frequency of each component to produce a spectrum. For the square wave illustrated above, we get the following bar graph shown below. Each bar in this "line" spectrum represents the amplitude of one of the frequencies contained in the original square wave. As in the optical case discussed above, we call this type of spectrum where the components only exist at particular points along the frequency axis a line spectrum.