Square waves are also one of those neat things that you can view on an oscilloscope. They can be approximated pretty well with sine waves; after all, a square wave is a signal that can be represented by an infinite Fourier series.
Note
A Fourier series is the sum of a series of sine and cosine terms named after the famous mathematician Jean-Baptiste Fourier (see http://en.wikipedia.org/wiki/Fourier_series).
The formula of this particular series representing the square wave is as follows:
