[Rock_Artist]

It's based on the following data:

The Mono/Mid Microphone gets the "Center/Middle" so it should get a clear straight picture of the sound.

The Side Mic use figure of 8 (the mic is positioned to the sides so it gets the left & right into a single channel)

Now M is the same.
However

M+S = Left
M-S = Right

Because we change the phase we get 2 phase cancelations.
One for left & one for right.

So we actually encode stereo....